Radio is a companion that is given to Luka, she is a parallel world's last functioning Makina.
Luka and the party have ventured through the third Tartarus and entered another dimension. Within this dimension, the world itself is being consumed by chaos. Both Sylph and Gnome inform Luka that their corresponding elements are dead.
At the entrance to the tower, the party is greeted by Radio. She is currently serving as La Croix's research assistant. She fills them in on the current state of the world: it's ending. The last human died 25 years ago; the last angel died eight years ago, and the last monster died six years ago. The only building still standing is this tower. Radio offers to lead the party to La Croix, on the third floor. She asks them to be careful as La Croix has created artificial monster girls to fight off apoptosis beings, and they will likely attack Luka.
By the time the party reach the top floor of the tower, there is nothing left. Just Radio, La Croix and the Cirque du Croix.
La Croix explains to Luka that their world will soon cease to exist due to the spread of chaos, and asks Luka to take Radio with him back to his world. She's grown fond of the machine girl and doesn't want to see her broken. Luka tries talking La Croix into coming with them, but having two La Croix's in the same world would increase the rate of chaosization, and refuses.
In the orignal timeline she never worked for La Croix rather to Promestein should Luka choose to surrender after the 4 spirits got sealed and Alice vanihsed due to the Great Six Ancestor's Seal. Radio meets Luka at the Drain Lab as this will be a game over for the player.
"Today is another good dAy. I am Radio, alsOKnown as a piece of junk."
Radio: You sMEll the same as master..."
Chrome: "Big sister... Well, I'm in your care, so please look after me!"
Radio: "Then I will get to work imMEdiately. The documents that were in your room have all been incineRAted."
Chrome: "I'm gonna turn this piece of junk into scrap metal!"
Radio: "HelLOLOLOLOLO GAGA... PII!"
Francesca: "Oh my, are you also junk...?"
Radio: "I am a piece of junk, nice to MEET YOU..."
Francesca: "We're better junk; we can still speak fluidly. I have a bit of sympathy for you..."
Radio: "Master... It haSBeen 14 years, 3 months, 18 days, 14 hours, 35 minutes, and 48 seconds."
Promestein: "Huh? ...I don't know what you're talking about."
Radio: "I don't knoWEither."
Radio: "But I feeLLike... I have a stronGSense of nostalgia."
Promestein: "That's pretty vague for a machine... Was your creator this vague?"
Radio: "HeLLo... I am model RD-0, often called a piece of junk. Pleased to meet yOU."
Robin: "An old fashioned fully autonomous mechanical lifeform, huh? By the way, do you even know what a 'piece of junk' really is?"
Radio: "It's a COmponent of a far eAStern ship... It's viTal to keeping everything afloat..."
Robin: "...Yup, that sure is what a piece of junk is. I don't think you'd float on water, though..."
Radio: "MistreSS Sonya..."
Sonya: "We're friends, Radio. You can just call me Sonya"
Radio: "Then please CAll me a piece of junk. That's what my beST friend used to call me..."
Sonya: "Were they really your friend...?"
“Master…" Radio is recalling memories of the past.
“Flies are flying around... Exterminating…" Radio fires a gun at random! (Play:Shooting Spree, attacks both enemies and allies 4 times at random)
“A switch on the top of my head... What is it supposed to be? It's small…" Radio causes a gigantic explosion! (Play:Explosion)
“Error in the roller function... Gyah!" Radio trips over nothing!
“Gaga... Piii! Gagaga…" Noises are coming from radio.
- Based on her conversation with Promestein in Pocket Castle, it is possible that her creator is Promestein from La Croix's universe.