Rizelmine

The day for the not so fortunate 15-year-old Iwaki Tomonori begins with him finding out that the teacher he had a crush on is now getting married to someone else.

Fed up with relations and marriage he rushes back home, to be pounced on by an unknown girl.

As it turns out the 12-year-old Rizel is part of a secret government experiment related to human genetics, an artificial human.

And to top things off, the government decided to marry him to Rizel without his consent.

Though his parents initially are also less than thrilled by having to feed another mouth on the family's low income, the government agents quickly assure them that all expenses will be paid.

And so, with the government and his parents to contend with, the dumbfounded Tomonori now has to live with a wife under one roof...

— written by foo2