I think Mawin's biological father is Than. Akin just took the responsibility of the child.... it's not sure the…
At the very beginning of the pilot trailer, there's a phone call with some girl mentioning she is pregnant with Than's child. It is likely that Kin wants to keep this a secret from Than so he disappeared to raise that kid alone. Thus I think it's still early to rule out the possibility that Mawin is Than's son.
I wish it was longer. But honestly, the reason this series is too short is because these boys talk it out every time a problem arises, which is a rare case in romance drama.
The black and white transitions before and after every flashback are really annoying. The audience are not too dumb to tell those scenes took place in the past. Besides, it's not like they went to college during the 60s or something.
(FYI, Suzume's plushie is voiced by Mitsuishi Kotono, the voice actress of Sailor Moon).