Overkilling means the character dies, not kneels on the ground. Team combos are an effective way of Overkilling a boss. A retreating boss is a boss that flees when too many of their comrades die or when they lose a certain amount of hp. I separated some of the characters into parts due to lack of room for a full explanation.
Viser - Overkill him in the first battle with him and kill ALL of his golems, also OK him in the second battle. Overkill all bosses that retreat.
Jade - Part I Overkill him in the first battle with him and defeat all his men. Overkill him the second battle.
Jade - Part II When given the option choose \"I wasn\'t really going to kill him.\" In Chapter 4 or 5 look for a quest for guarding a gold transport.
Jade - Part III Jade will be there and will flee. Go to the guild and look for a letter from Jade. Fight him and he\'ll join.
Echidna - Part I When given the option choose \"You\'re about to find out!\" and then Overkill her in the battle that follows.
Echidna - Part II Spero must have his final rank (Samurai) by getting his legendary weapon and then when you fight Echidna the second time Overkill her.
Tia - Part I Do not let Tia die in ANY battle she\'s in. Except the first golem battle. Depending on if she dies there, she\'ll appear in a different spot.
Tia - Part II Read all of her letters. After getting letter 12 she\'ll appear in Silva or Aphen.
Submitted by Michael Osuere