My question is…why not both?
We’ve spent more time with Isamu thus far and the MC knew him in the past which makes him an attractive prospect to some for various reasons (including the fact that some people like seeing love overcome complicated pasts or something like that). Some might even just like older men. I’d think he was the more popular of the two, but it’s not like I have data on that.
I myself am interested in seeing a romantic progression between one of my female MC since I find their past is interesting.
Dai is someone new, but he’s young and (from the sound of it) a nice kid. Haven’t seen the update, but he could be interesting to people as well.
I think there could well be a demographic for both.