Alto Goldfield is a student at a magic academy. He's trying to become a master magician, but can't seem to pass the summoning exam. On his last day to perform the ritual, he find a strange book in the library. From this book he finally manages to summon something: Vermeil, a big-breasted, older sister-type demon. And she falls for him. A series that is as horny as it is wholesome. While Vermeil is a huge tease, she is also incredibly sweet and loyal. Alto's not so bad either, since he grows to care about Vermeil a lot, grows in power as well, and isn't afraid to lay a smack-down on anyone who tries to harm Vermeil. Not that most CAN harm her. She's incredibly powerful. Oh, and there's a tsundere childhood friend and a yandere senpai with a dragon. Enjoy.