tobio is totally clueless in here but it suits his character...
oikawa x tobio kageyama ship. apparently they are dating and kageyama's skin color changes with the season. with a fair warning from tsukishima, kageyama wonders why they called him a chamelon so he asks oikawa. then they have sex. turns out, when kageyama is pale and not "excited" his hickey marks can be seen which he doesnt realize. when he is excited his skin turns red so the hickeys are visible.
Haikyu!! Dj - Chameleon