For those who have read the series and pondered about who the father might be. I have reread multiple times and have had an EPIC SPASM once I've found out. The dad is Mika. In volume 5, Tobina has given us proof of who the father is by revealing it in the ending. For both in the ending and on the cover, Mika and Takamichi both have the same exact ring on their fingers. >U< .... !