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.
Precocious Crush : Kotarou gives a lot of hints that he has a crush on his nii-chan, like getting sad when Ryuuichi was going to kiss the twins, or getting depressed when Usaida interrupts his 'alone time with nii-cha' (it's just Ryuuichi reading him a story book). Usaida lampshades both occasions, saying how Ryuuichi shouldn't 'cheat' in the first case and apologizing for ruining their 'lovey-dovey' moment in the latter. Both him and Kamitani also showed concern about the brothers' relationship. Ryuuichi being Ryuuichi, he doesn't get it at all.