Thanks for the chapter!
Yes the MC has achieved the dream of many boys wishing to hand in their v-card by summoning a succubus! (Btw, where are her wings?) However, due to age restrictions set by the regime in an effort to increase summonings she's not allowed to have intercourse with him, even if commanded, until his 18th birthday. Seriously though, based on her personality I wonder if she really is a bad person or if most of the bad things she did was due to commands/orders from her previous masters rather than her own volition. Seems like the summoning forces her to obey any command once the contract is set. After all, rather than hurt or kill Lilian or Sylph instead Vermeil overstimulated Lilian's pleasure. A truly evil person would have gone too far with punishment for going against her and/or her master or just for kicks to showoff.
MC is an idiot. A book falling from a shelf never noticed before made from old wood and nonlinear sides when the rest of the library has well maintained, newer, perfectly straight shelves should be extremely suspicious. Obviously it's enchanted to appear only under certain circumstances and not for common use. In any case, are unicorns considered the lowest summons for some reason like will only make and maintain a contract with a virgin or something? From sound of things it'd be like getting a lvl1 slime for a summons. It's interesting that he can only summon and contract high level creatures due to his mana being so thick and dense it's poisonous to the average summon creatures. In any case, Vermeil seems like she'll liven his life up a lot, if she doesn't kill him by draining him dry or causing everyone else to do him in out of jealousy. Granted she's "evil" but seems more anti-authority and free spirited than evil. If she really was evil incarnate she'd have thanked him for freeing her by killing him quickly and painlessly rather than contracting with and teasing him. Seems to really like him considering all the hearts floating around, is cute, and fun to tease. Lillian looks like she's going to blow a gasket in jealousy though. Strange that contracting devils is bad but humans are barely acceptable. What does a contract do anyway?
Can see how the school avoids responsibility and encourages favoritism. Basically saying strong duelists can force others to do what they want and the school won't interfere. Thus encouraging results by giving more privileges and protection to those who excel over those who don't.