Finally confirmed not canon. It was kinda obvious when Mikhail and yuri appeared at the onsen actually but at least now we know for sure.
But in the onsen chapter it is implied that aki and fei were emailing each other. Maybe author just want the readers to know that fei and aki still contact each other after the hongkong arc....
The onsen extra looks symbolic more than canon, and yeah, it's implied aki and fei were in contact through e mails, texts, also in Fei's novel there's this implication.
I can't believe how many idiots out there actually believed the onsen extra was canon. There is an actual interview in print where Yamane-sensei says she did it as fanservice since fans were asking for a threesome. However, there are canon bits interspersed in it: like Aki and Fei comunicating and Mikhail and Yuri' appearances, for me at the time that was foreshadowing on sensei's part. Mikhail has already turned out to be back in the game and one of the major key players, as for Yuri....I have never belived him to be dead. That eyepatch is from getting shot in the eyeball by Asami for sure, LOL.
I lowkey worship the onsen part
It might be canon in the future, a great sandwich ah mye gad!
although I lowkey ship asami and fei long, i'm very much grateful for fei's help. finally asami and akihito met! ( T﹏T ) now, now, i hope to see them do it soon
ps. so the onsen side story was kinda not canon? cuz akihito said the last time he saw fei long was back in the cruise ship