People here have no idea what they're talking about. This isn't "hard" netorare, this is almost 100% pure netorase, with netorare only in the bad endings. The heroine is an alchemist, which in this world apparently means making homunculi out of monster semen in her womb. She's an apprentice (virgin) at the start of the game, but when her master goes missing, she's forced to finally become a fully fledged alchemist. But before she starts gathering semen, she decides to lose her virginity first to the man she loves, the protagonist. After this, she can charm monsters with magic, convince them to sex her, and then rely on the protag to retrieve her. To actually perform the alchemy though, she has to have sex with the protagonist. And the entire game, outside of the bad ends, the person she loves the most is the protagonist and this never changes. It's very similar to Mijishi's other games.
Yes. That unlocks the second tier of alchemy. It convinces the heroine to stop holding back. Apparently, she can also make drugs to boost the stats of her homunculi, but it's more effective if she gets the semen from someone other than her alchemy partner (the protag). Mind, this also unlocks the system for the protag to have sex with random girls in town. Just as the heroine is whoring around, the protag can pick up whores, duel knightnesses, and convince random school girls to have sex with him.