Oh noes, is his sister's friend also entering the fray as a potential love interest? Don't develop into a harem, please. No harem tag, but on the other hand, the lack of a romance tag is also concerning for me... (I swear this had it the last time I read this... what happened?)
Interesting to see Hayato get his turn at becoming uncomfortable at the idea of Haruki being with another guy and taking some awkward action, Haruki took some awkward action herself last time when he and Minamo were busy doing their gardening stuff.
Kazuki appears to be going into full love rival mode, and likely wants to see and know better who he's up against. It would be nice for that to be subverted though, and have him actually only want to be friends with him, and even better if he was in love with someone else. But I think that's unlikely. I'd be surprised if that was the case.
Though it puzzles me how we're getting love rivals on both sides to push a romantic subplot when the romance tag is missing...?