Räikkönen no Nettaigyo

Sekohara finds himself joining the Tropical Fish Club at school, which at this point, only has the founder as its only member, a mysterious girl named Räikkönen. She is a self proclaimed witch, but Sekohara doesn't believe in the nonsense until she is able to turn an angelfish into a human girl with the use of her homunculus alchemy. Räikkönen's goal is to see what happens when a human mates with the transformed fish, but the more time Sekohara spends with Räikkönen, the deeper the emotions get. More and more people close to him get involved in the magical experiment she is conducting.

(Source: MU)

Included one-shot:
Volume 1 (Kanzenban): Noroi no Megane