That is a NICE arrangement. At first, given the picture of Atsuka, I thought it might be from the second season of Hibike! Euphonium, but then I saw it was posted in March of last year. I'm going to pass the link to a Japanese friend and see if he can find the name of the arranger.
David Bjornstad
1923 Conn New Wonder 86I, Bach 6 1/2 AL
2018 Wessex EP100 Dolce, Denis Wick 4ABL
2013 Jinbao JBEP-1111L, Denis Wick 4AM
2015 Jinbao JBBR-1240, Denis Wick clone mouthpiece of unknown designation
Cullman (AL) Community Band (Euph Section Leader)
Brass Band of Huntsville (2nd Bari)