Kazuya is one of the seven heroes of the Collaboration Scenario. He comes from the game Shrift, alongside Lampas, Mukuro and Daji. Like most of the other characters in the Collaboration Scenario, he starts off without any levels in jobs or races until he reaches a proper job change book.
Kazuya first appears in chapter 2 as he wakes up from a bed, surprised to see himself in an apparently medieval house. He feels worried, as he feels extremely vulnerable alone. Still, he manages to recover his gun, and checks his environment. When he checks himself in the mirror, he slightly panics as he notices a crest on his hand. He decides to focus on getting a grasp on the situation.
When he enters the hallway by leaving his room, Myusca's voice echoes in his mind and informs him (and several other people) that they will be turned into her food, unless they manage to escape. As he starts moving, he gets attacked by a Lampas. He is surprised to see one of them here, and wonders if its appearance comes from the work of Hecate.
When they start chasing him, Kazuya starts to run away, and, after crossing several rooms, notices a monk boy running away extremely fast. He decides to try to find him to protect him. As he continue progressing, he notices a Lampas light, silently informing him that a human met his demise here. He notices he is trapped into a room loop, and manages to extricate himself of this trap by leaving by the way he entered.
He's then ambushed by another Lampas who blocks his way. He attempts to push her back, and is surprised when he casts a fire spell at her, burning her. He stops the flames with water from a well-placed pot. The Lampas let him pass, but guilts trip him for having burned her. He realizes that she will pester him to follow him even if he ignores her, and welcomes her in the party.
Kazuya then interrogates her to know why she's here, and is surprised to learn that just like him, several Lampas were sucked by a black hole vortex. He has difficulty accepting that this is a parallel world at first. He receives additional information, namely that magic is easy to use in this world which is why he's able to use it once again. He then refuses Lampas' lewd offer.
As he keep trying to catch up to Hakunen, Kazuya meets his first Spirit Fox. He presents himself as a Demon Hunter when the latter tries to seduce him and tells her to run. The result ends up being too effective, as she runs away in a panic while screaming after being beated once. Unfortunately, Kazuya reaches a pub where tens of them are drinking, and is aghast when they take him for an exterminator. He's forced to fight a lot of them, although most of the lot just falls unconscious drunk without fighting. Right afterward, a shocked Hakunen is surprised by the large number of supposedly dead foxes around, and flees Kazuya in fear. A clearly dumbfounded Kazuya is determined to chase him to at least clear this misunderstanding. Eventually, he manages to free him out when a large group of Spirit Foxes gathers to block the monk boy's path, and finally manages to get him to listen to what he has to say.
As the duo discusses, they realize they both got sucked in this world by a vortex and are in the same delicate situation. Hakunen then joins Kazuya, and tells him that he's looking for his master. When Hakunen blushes, Kazuya thinks there is a forbidden love between both of them.
When Hakunen tells him that he himself is bad at fighting, Kazuya tells him that he will defend him, before being flabbergasted when Hakunen proceeds to crush a boulder in a single punch. After crossing several mazes, the party ends up meeting a young man who tells them they're in the village of Finoa before unfortunately falling prey to Myusca. Realizing that they're outclassed, Kazuya leads the party away before running into a large group that took refuge. However, Myusca follows them, sucks dry a few people, and leaves to enjoy the party marinating in their own fear.
As they get close to an exit, the party encounters the White Rabbit. While the other party members are wary and wonder if she's an ally of Myusca, Kazuya recognizes that she isn't an enemy. He then receives an explanation about the Seven Heroes, the crest being the Proof Collaboration and the "Queen of Dreams". Kazuya accepts it and correctly deduce what's happening. Afterward, when Hakunen reveals he is married, Kazuya is shocked and become extremely formal for a short time. However, he also notices that the White Rabbit let slip some information that she shouldn't know.
Afterwards, the party soon meets Myusca again and is forced to fight her. They barely manage to scratch her when the Proof Collaboration on the back of her hand reacts, dumbfounding them at the idea that she could be one of the Seven Heroes before hey decide to run away while she's still surprised. However, once outside, they end up running into Nemea and Vinum.
Kazuya identifies the former as being just as dangerous as Myusca, while he considers that the latter is on a league of her own. Amused, the two succubi decide to leave and continue wrecking the village. While Hakunen is aghast, Kazuya decides that they have to keep moving on if they want to have a chance to survive.
When they enter the next house, Kazuya is surprised by the sight of several Mukuro dolls attacking the villagers. When they don't recognize him, he understands that they're just machines. He then explains to Hakunen that Mukuro was a girl who died in loneliness as a sacrifice and whose spirit possessed a doll to make contracts with her partners by squeezing them, although these ones seem different. Kazuya hears rumors about the Monster Lord having organized the attack in Finoa and he is surprised that Luka's world has a Demon King like his world.
The party later runs into Nemea again as the latter is draining a young boy to death. Understanding that they're outclassed yet again, the party is forced to escape.
Afterwards, the party encounters Vinum, who is too busy reading and doesn't want to be disturbed. The party is forced to sneak through a mess to not catch the attention of the succubus.
After sneaking through, the party encounters several non-functional Mukuro dolls, and it is revealed that Kagetsumugi is responsible for mass producing them for the Alliance. The party is cautious when they encounter her, and she unleashes a Mukuro who still has some memories of Kazuya and shows signs of life. Kazuya calls her by her old name, Akane, which triggers her old memories and forces the party into a fight.
Kazuya then gladly welcomes the conscious Mukuro back. Once the heroes have beaten the doll, they ask Kagetsumugi if she will be their next opponent. The small puppeteer answers them that she will take her leave as she delivered the dolls to the Alliance just like she was asked, and let Kazuya recruit Mukuro for the sake of the doll's happiness. As she leaves, Kazuya asks her if she's a puppeteer or a puppet, upon which she answers that she is "not a puppet" while displaying her monstrous nature for a short instant before disappearing.
Unfortunately, not long after, the party falls on Vinum and they realize they must once again run with all their might. As soon as they escape, they fall on Nemea and are forced to fight her. Just afterwards, Vinum and Myusca show up, cutting any chance the party has to retreat. Fortunately, they are saved by the intervention of Magatsu, Lauratt and Rigeo.
Before the succubi leave, Kazuya asks why Myusca has the Proof Collaboration on her hand. She answers that she got it when she arrived, before being corrected by Vinum who reminds her that she got it from her first victim who was supposed to be the hero of their world, which surprise the succubi as he was incredibly weak.
Afterwards, both groups introduce themselves to each other. Kazuya is surprised to see that Hakunen's master is a beautiful oni, which Magatsu exploits to further tease her apprentice. As they hear from Rigeo about the Château des Romances, they decide to fully focus their attention on going there.
When the party arrives in front of the Château des Romances, Kazuya is impressed by the size of the place, but steadies himself. When the party meets the first group of Nightmares, he realizes his lack of pleasure skills make him useless against them and forces him to remain behind. During their exploration of the castle,Kazuya is shocked to see even angels like Cupid and Valkyrie in the castle, as the love angel was invited by the Queen of Dream. He also warns the party that they should expect a lot of mimics. As the party pushes toward the throne room and Fulbeua, they are blocked by a barrier that needs to be deactivated first. In the kitchen, they meet a nightmare who's ready to tell them where the switch in exchange for a little energy from one of the males. Afterward, the party comes face to face with Fulbeua herself, and attacks her in hope of getting information about the dimensional gate location. However, Musette steps in and asks Fulbeua to deal with the intruders appropriately. As conflicts rise between the two of them, Kazuya decide to resort to their best strategy: To run away with everything they got.
As they think they managed to escape the throne room, Myusca, Nemea and Vinum appear to chase them, with Vinum teleporting later again to block the exit. The party is forced underground, and fight Vinum who is alone.
After successfully repelling her first assault, Myusca and Nemea step in to finish the party. However, Luka and his companions arrive to save them. As the situation becomes more chaotic, Myusca gets captured and Vinum negotiate their retreat. Kazuya jumps in, and uses the opportunity to have Myusca transfer the Proof Collaboration to Luka.
He accompanies the party when they go search for Gilgorn in the basement of the castle. Once everybody's back to the Pocket Castle to regroup, Kazuya remarks that they're lucky to still be alive as they had rushed in without a real plan. When he hears that most leaders have been brainwashed once, he wonders if this world isn't in "hard mode."
He supports the party when they finally assault the castle itself with Gilgorn's power. When the party finds out a note from Dr Yui, Kazuya apologizes for forcing the party to make detours as the good doctor mucked up the transfer coordinates. After they beat Fulbeua again, Kazuya ominously tells Luka that "she's lying."
When the party finally reaches the White Rabbit and the room where the other version of her should be, Kazuya mysteriously asks Luka if he's noticed. When Luka hesitates to open the door, Kazuya exposes the White Rabbit who was Daji all this time, and tells that the room was certainly one of her trap filled with familiars. After the team beats her, he remarks that she wouldn't be so crass as to attempt to stab them in the back again.
Afterward, he successfully beats Est with the six other heroes thanks to the power granted by the Proof Collaboration.
When everybody is back in the Pocket Castle and realize that they can't go back to their world, he thinks that the idea to destroy the portal to restore the situation was likely another one of Daji's lies. Like everyone else, he accepts to help defend the world and hunt down the other members of the Alliance of Est.
In the Post-Collab, he regularly intervenes. He first steps in when the party has to chase Daji in Yamatai Village, as he knows how dangerous she can be. When the party finds her and beat her, she threatens to show her real power, but Kazuya convinces her to stand down and to join the party.
After the party beats Fulbeua again and she asks them to bring something more beautiful than her, Kazuya remarks that it's just like the Kobayashi Maru scenario, which makes Luka wonder what he's talking about.
In the Succubus Prison Trio recruitment sidequest, as the heroes are paired with their heroines for the "Sex Rooms", he ends up with both Lampas and Mukuro who glare at each other. When the party reaches the "Karaoke Handjob" challenge, he remarks that he already participated in a game like that, and gives it a go after Hakunen fails. However, he only ends up scoring 36 points, and is embarassed when Lest does better with 38. When Luka's companion decides to bring in Saki, he's amazed by the idol's skills. When they reach the fifth challenge which is also the fourth "Sex Room", Kazuya ends up pulling the short straw. As a result, Mukuro and Lampas enter a tug-of-war contest before doing another straw pull which Lampas wins. However, after the couple enters the room, Mukuro soon follows and Kazuya is reduced to a ghastly, emaciated barely-living body after both monsters nearly suck him dry. Fortunately, he does manage to recover.
Kazuya: “Would you be okay with taking me with you? I'd like to see more of this world.”
- Double Slash - Sword Skill (Physical 260% Att), Target: Foe
- Double-Edged Cut - Sword Skill (Physical 660% Att), Target: Foe, Effect: 1/3 HP Self Damage
- Double Tap - Gun Skill (Physical 180%*2 Dex), Target: Foe
- Spray & Pray - Gun Skill (Physical 320% Dex), Target: All Foes
- Relax - Target: User, Effect: 60% HP Recovery
- lvl 51: Hot Limit - Black Magic Skill Target: User, Effect: +50% Att/Mag/Dex (5 turns)
- lvl 52: Cool Calm - Black Magic Skill Target: User, Effect: Sleep/Confusion/Pleasure Status Immunity (5 turns)
- lvl 53: Sylph Storm - Black Magic Skill Target: User, Effect: +90% Eva (5 turns)
- lvl 54: Vortex Step - Black Magic Skill Target: User, Effect: Sword/Gun/Black Magic Skill speed up (5 turns)
- lvl 55: Delta Aero - Black Magic Skill (Wind 1000% Mag) Target: All Foes
- lvl 56: Hell Break - Black Magic Skill Target: User, Effect: +40% HP/SP Regen, +10% MP Regen, Stun Immunity (10 turns)
- lvl 57: Frozen - Black Magic Skill Target: User, Effect: +50% HP/SP, 50% Pleasure Resist (10 turns)
- lvl 58: L-Period - Black Magic Skill (Magic 1400% Mag), Target: Foe
- lvl 59: Sylph Trick - Black Magic Skill Target: User, Effect: -50%SP/MP Cost (10 turns)
- lvl 60: Rising - Black Magic Skill Target: User, Effect: +100% Mag Eva, Bind Immunity
Collaboration Scenario - Post Collab
- Hero of the Seven World - Special Ability (All Attacks gain the Pleasure Attribute)
Time Loop - Promestein's request
- Kizuna's Ring - Special Ability - Allows the summoning of friends from My Room. Also increases Summoning damage by 15%, and Summoning skills use Dexterity in place of Magic.
- Barghest - Summoning Skill, (Physical 1400% ^ of Mag, Dex), Target: Foe, Effect: +150% to Bleeding, Do nothing 25% of the time.
- Lampas (Ivy Shackles) - Summoning Skill, (Pleasure 1000% ^ of Mag, Dex), Target: Foe, Effect: +150% to Bleeding, HP Drain 50%
- Iron Maiden (Saiga Tear) - Summoning Skill, (Lightning 1000% ^ of Mag, Dex), Target: Foe, Effect: +150% to Bleeding
- Empuse (Funeral Dance) - Summoning Skill, (Physical 360% ^ of Mag, Dex), Target: 4 Random Foes, Effect: Bleed (25%), +150% to Bleeding
- Mother Rabbit (Affectionate Cradle) - Summoning Skill Target: All Allies, Effect: HP Recovery 100%
- Haru & Liz (Beast Dual Claw Tune) - Summoning Skill, (Physical 360% ^ of Mag, Dex), Target: 4 Random Foes, +150% to Bleeding
- Mukuro (Gyro Flash Drive) - Summoning Skill, (Physical 1000% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Nina (It's Showtime!) - Summoning Skill, (Pleasure 1000% ^ of Mag, Dex), Target: Foe, Effect: 40% SP Regen, +150% to Bleeding
- Echo (Saiga Agni) - Summoning Skill, (Fire 1000% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Sphinx (Saiga Frost) - Summoning Skill, (Ice 1000% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Arachne (Lewd Web) - Summoning Skill, (Pleasure 1000% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Titanoboa (Evil Snake's Strike) - Summoning Skill, (Physical 1800% ^ of Mag, Dex), Target: Foe, Effect: +150% to Bleeding
- Camazotz (Saiga Garuda) - Summoning Skill, (Wind 1000% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Daji (El Delteca) - Summoning Skill, (Dark 1400% ^ of Mag, Dex), Target: All Foes, Effect: +150% to Bleeding
- Rebellion K - Gun, Can fire elemental bullets
- MTTK Special - Gun, Critical Rate +25%, Critical Damage +50%, Can fire elemental bullets
- Cane of Wisdom - Rod, Ignore Fire/Ice/Lightning/Wind Resistance
- Fan of Demonic Purification - Magic Sword, Resist Elemental Damage 50%, Fan Property
- Rear-Mark 42 - Armor, Physical Resistance +50%
- Calming Jade - Accessory, Attack/Magic/Dexterity +30%, Nullify Stop/Climax, All Stats Up when Mukuro is in the Active Party(First Four)
- Kazuya's trait and personality is the one of the end game true mercy run: He is friendly with another Lampas in his home dimension, makes regular references to the other recruitable girls, (including Sphinx and Dr Yui, a scientist in the vein of Promestein), and knows about the nature of Daji's trap, which requires to befriend her and everyone else in the game.
- Kazuya nearly breaks the fourth wall when he sees his first Spirit Fox, nearly calling it a Pikachu but refraining from fear of "summoning a terrible entity."
- He will also address the player directly during the first looping maze in chapter two if you continue looping between the rooms without actually progressing.