You play as one of the regular enemies from the first game, who, this time, must go and hunt humans. Lucifer (Satan in translation) has put out a reward for human girls, and it’s up to you to bring them to him.

See also:

Rosario+Vampire: Tanabata’s Miss Yokai Academy Reserve X-Note Tokimeki Memorial Girl’s Side 1st Love Plus Storm Lover Kai Human Tanks, Charge! War of the Human Tanks