These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Les Yay: Eri and Yakumo make up after the play in the second season with a fast-paced dance that ends up with Yakumo coming out on top in a surprise reversal. The crowd goes wild.◊
Not to mention Itoko being very close with fellow teacher Youko Sasakura.
Yakumo is a frequent victim courtesy of Akira and Sarah.
Akira in general hints heavily towards other girls.
OT3: The Kid's Meal faction (for those just passing by, that's Yakumo/Eri/Harima). By the end of the manga, Yakumo is living with Harima, and Harima is engaged to Eri. Maybe.
Mary Sue: Yakumo has her moments. She has telepathy when nobody else in the manga has powers like that, has boys (and girls) gushing over how beautiful she is almost constantly, is a Friend to All Living Things, an excellent student and becomes involved in the most prominent Love Triangle of the series with Eri and Harima. It's especially jarring when Tenma is supposed to be the main character. Might be part of the Genre Deconstruction, since everyone likes her better than Tenma.