Critical Ecstasy is a specific term used in the game, describing the heavily weakened state of a man when forced to ejaculate by a monster. Whenever he orgasms, he suddenly becomes frail and loses the ability to fight back against the monster.
The term is stated by a Knight within Ilias Village, describing that ejaculation drains one's fighting spirit, according to scholars. In other words, if a man comes, his mind and spirit surrenders, and the monster will be able to have their way with him.
No matter the difference between the level of man and monster, the man will surrender if Critical Ecstasy is reached. For example, a level 3 Imp can have her way with a level 59 Luka if she can make him come.
It is heavily implied that Critical Ecstasy has little to no impact against most monsters. Vampire Girl orgasms multiple times in her rape scene but remains in control of the rape with no signs of weakening; and Siren looks forward to her orgasm (which never happens), implying that ejaculations have little effect on her. However, Granberia seems to be susceptible to pleasure, although this may be due to her inexperience with sex.
It is unknown if human women are vulnerable to Critical Ecstasy.