... explaining the motivation of teasing is tacked on, pointless, or forced? It's not exactly uncommon to see Rin's canonical attachment to Maki read as some degree of interest, and revealing that Rin is teasing Maki because she's feeling kinda jilted makes sense for this story. "I get that she feels that Nico is especially important to her — but it hurts that she doesn't feel that I'm special to her at all."
(I mean, Nozomi would instigate things without any personal stake in the situation, but if Rin weren't feeling hurt, she probably would have just bugged Maki to set personalized ringtones for everybody, instead of the focused needling here.)
Tacked on would be something like the back half involving Honoka coming out of nowhere to complain.
