Hiiragi Serori has to investigate Ryuumeikan as part of a request by a mysterious client. Obviously, this intrusion doesn't sit well with the rule-abiding Kurogane Otome.
Nee Shiyoo! VS Tsuyokiss is a crossover between Tsuyokiss and Nee, Chanto Shiyou yo!, first released in Tech Gian, where the characters from both series go on a rampage in Matsukasa!