Critical Ecstasy is a specific term used in the game, stated by a Knight within Ilias Village. Whenever a man reaches the brink of ejaculation, he is forced to submit.
Scholars have concluded that ejaculation drains one's fighting spirit. In other words, if a man cums, 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.