In Succubus Research Diary, Serena is a daring explorer who meets a kindhearted succubus named Nerisha. They met by chance in the depths of the Underground. After meeting each other, they strike up a very unusual deal. It's a deal that requires both of them to have lots of sex. As you might imagine, sex is super hot, and it's fascinating to watch girls like these explore their lesbian desires. As they lick and do everything else to satisfy the other, they discover a world of sexuality neither could've imagined.