liam

i know i tend to overanalyze everything and that by virtue of being a non-native japanese speaker i inevitably lose some of the cultural nuance but bear with me for a second:

as we already know, most japanese people their age would usually address each other by their last names + -san or some other honorific because politeness is crucial to their social interactions, with exceptions being things such as nicknames ( “ushiwaka” / “omi-omi” ), when the honorifics are dropped altogether ( “hinata” ), or when they’re deliberately trying to be rude ( oikawa’s “tobio-chan” ). 

so for sakusa to call ushijima “wakatoshi-kun” aka his first name plus an honorific, and for ushijima to not mind in the slightest, it means they must have a really close relationship. another very important detail to keep in mind is their age difference–sakusa is one grade below ushijima in high school, which means he should have been using -senpai or -san. 

from this panel (ch 394) we know that despite sakusa’s attitude and bluntness while speaking, he’s not a rude guy. since he was young, he’s been alert to social cues of politeness, like when he tells komori to stop pointing at people because it’s rude. so he’s well aware of what would consist of crossing the line in regards to overfriendliness.

i find it fascinating that he calls his own team captain–whom he met in a similar way to ushijima (the lint roller thing, both being appreciative of the other’s cleanliness, blah blah) and whom he’s definitely spent a lot of time with because iizuna could accurately tell what sakusa was thinking right before the exchange pictured above–“iizuna-san”: the last name plus honorific combo. and they went to the same school in tokyo, whereas ushijima was all the way in miyagi doing his own thing.

which can only mean his relationship with ushijima goes beyond simple admiration and acknowledgement of each other’s talent. another thing to consider is the other person who calls ushijima “wakatoshi-kun” is tendou, and they’ve announced publicly they’re best friends.

from this panel, we find out that they participated in the same training camps several times (and we know from the karasuno-nekoma-fukurodani training camp arc that this is a great opportunity to get acquainted with people and build long-lasting friendships!) and that they seem to genuinely enjoy each other’s company. they have a really special relationship that’s under-explored in fandom and i’d like to see more of it in fic and art!!!

tl;dr: sakusa calling ushijima, his senior, by his first name, and ushijima approving of this, puts them on the same social level in terms of their relationship and feelings towards each other, which means they are very, very close.