kibishii onna joushi ga koukousei ni modottara ore ni deredere suru riyuu

The Reason Why My Strict Female Boss Turned Deredere on Me After Turning Back into a High School Student: High School Life Where We Redo Our Mutual Crushes

Light novel series by Tokuyama Gintarou, with illustrations by Yomu. Premise of the story is exactly as described by the title and 'sub-title'. 'Nuff said.