Vampires of course.

"Well, I think it would be most fitting to teach you about Vampires first," Moka giggled, slipping off her skirt, and sitting in her panties and bra.

"Of course," Tsukane chuckled dryly, holding his bleeding neck. "Best start with what you know best."

"Obviously, I'm not going to tell you all of the secrets of Vampires," Moka then told him. " A lot of it is secret for a reason... But there shouldn't be any harm in you learning common knowledge. Monsters can be violent after all, and won't hesitate to use this sort of thing against me, so we ought to stick together."

"I can agree with that," Tsukane replied.

"As you know, Vampires mostly drink the blood of others to sustain ourselves. We got by without killing humans for a while thanks to transfusion packs, avoiding the need to drink directly, but I must say, it is much better to drink directly from you..." she purred, causing him to quickly cover his neck.

She giggled at that, and said, "I already told you that Vampires are considered the be the most powerful of humanoid monsters, but we do have some weaknesses... For instance, you already know I sealed off my powers with this Rosary... There are a few in history that have been defeated like this, by a Rosary being placed on them in the middle of a fight, so that's something we have to try to watch out for. Water also saps our strength when we come into contact with it."

"Wait, how do you stay hydrated then?" Tsukane asked.

"We drink other things. Water is fine as an ingredient in drinks for us, it's only if water is pure enough that the "purification" properties of it are dangerous for us," Moka replied.

"Ah," Tsukane nodded, and Moka continued to lecture him on some trivia about vampires that most other monsters knew. The night soon ended, and she returned to her room, and Tsukane headed to bed.