After a good night's sleep, I am a little more iffy on how the Ruki/Sacchan relationship ended up. Maybe it's how quick Sacchan starts to smack people. It's played for laughs, but domestic abuse isn't funny. The whole thing about Ruki getting her pride crushed throughout the story, how other characters were calling her whipped at the end, and lots of other things are worrying signs of a potentially abusive relationship. It does seem that Sacchan came to love Ruki before the end of the story, but love is straight up not enough for people to lead happy and fulfilling lives.
I dunno, maybe I'm overreacting. I still really liked the series.