Kaoru, who has been repeatedly characterized as an extremely out of shape, unathletic loser, out-running the class president. Kaoru taking the class president's "you're not worthy of Nana" spiel with a resigned "What are you, an idiot? Of course I'm not" and turning it back on him.
"Some blockhead like you is no more suited to Nana than I am! You'd better learn your own place! Just give up before Nana dumps you anyway, idiot!!"
Kaoru turning into a bit of a Guile Hero to save Nana when she confronts two shoplifters while she's tied up. He knows that he can't take them head on, so he grabs one of their wallets so they chase him.
Tachi going to Kaoru's and making a lot of noise as if she and Kaoru are having a breather... all to convince Nana to come over so they can start the actual breather. And it works perfectly.
Kaoru gives an absolutely EPIC"Reason You Suck" Speech to Nana's homeroom teacher, class Kohais and fellow student council members for constantly taking advantage of her and dumping all their work on her because they know she'll say yes, and ask them if they ever think about how much stress they're putting on her. The very next day they all do the work they dumped on her and trip over themselves to apologize to Nana.
Arguably the best part is when the StudentCouncilPresident thinks about this and realizes that the ugly, socially withdrawn, class-failing pervert cares more about Nana's well-being than any of the rest of the beautiful, high-achieving people that went looking for her.
Kaoru: Even if I knew where Nana was I'd rather DIE than tell any of you!
As chapter 96 shows, when Kaoru actually bothers, he can be not just bizarrely inspirational but also intelligent. He manages to go from the highest 80% of his class to just outside of top 50%. That's a lot of improvement in such a short amount of time.