After a match with Aoba Johsai, Oikawa decides to take Yamaguchi aside, talking to him a little, a normal conversation, however, Tsukishima didn't seem to like it very much, even if he didn't show it. Everyone could tell he was jealous, he was LITERALLY looking at Yamaguchi and Oikawa really pissed, Oikawa for example, didn't care much, he just kept talking and praising Yamaguchi's (serves), and Yamaguchi seemed proud of himself, since Oikawa was a third year and Yamaguchi was a first year. Anyone would have felt flattered since he was being praised by a Senpai and Yamaguchi was no different, he was smiling from ear to ear with a bit of a blush

Oikawa smiles at Yamaguchi and puts his hand on his head, ruffling his hair, leaving a piece of hair sticking up a little. Then he smiled at him and went to talk to some of his teammates, while Yamaguchi, who was still blushing, didn't even notice that Tsukishima was there, he came to stand beside him and Yamaguchi jumped, surprised, but upon seeing it was him, he relaxed.