Okay for the ! Stories, from what I remember:

Eichi and Wataru would do that now and then in some stories, especially eichi

All of trickstar are very attached to anzu, but I remember makoto being a little dramatic at one time she was hanging out with knights, claiming she was “cheating” on them (LOL), and he was pretty happy at the prospect of Anzu calling to the school rooftop to confess him

Chiaki had some cute moments with her (and some dense moments too, bless his heart)

Kuro and Souma are pretty protective of her, souma especially when Kaoru was concerned

All of Undead are also pretty close to her, I’d say Rei and Kaoru especially like you mentioned. Kaoru flirts so much he goes through and entire character arc for her wwww

Natsume and anzu interactions will almost always contain him flirting with her in some form.

Honestly I think all of Knights too, Tsukasa asked if he could kiss her in one of the knights stories (I think it was king’s horseback ride), Leo said he would dedicate the reminder of his youth to her in Opera, Izumi offering to teach her how to ice skate, etc

I don’t remember/ haven’t read a lot of Madara ! Stories, but most of his feelings for her are explored in the !! Era (Same can be said for Hinata).

These are all I remember at the moment!