Album title: Niizuma wa Sailor Fuku ~My Darling is the Teacher in Charge~ Original Soundtrack
Composer: Hiroki Kikuta
Released: 2005
VGMdb link (http://vgmdb.net/album/4695)

Title is sometimes written as:
- Ni ~ Duma Wa Sailor Fuku
- Ni~dzuma wa Sailor Fuku
- Nidzuma wa Sailor Fuku

Did you ever manage to find this soundtrack?