Ch.1-5: Straight seme x kindergarten teacher uke. Uke only has one-night-stands, while wearing a wig, but then meets the uncle of one child in his nursery and gets recognized.
Ch.6: The two children from the nursery grow up and are now step-brothers in love with each other.
Def. re-read, love it!
Shou Sensei no Ecchi na Himitsu