Bringing Luka to the brink of the edge, a simple stimulation will bring him to ejaculation. This requires 0 SP, and will bring Luka’s HP to 1, however it will be his turn again. This technique is merely a joke by the developers and is another way for Luka to lose instantly besides Surrender or Request.
Edging is not taught to Luka; he possesses it at the beginning of the game, but only if Chapter 2 is installed. If the game is a Chapter 1 only version the skill is unattainable.
After edging the opponents face will be the same as after the "low health" remark (the extra bit of text you get when you are on low health).