I was thinking maybe sensei was a bit older than Daphie guessed. IDK how studying massage therapy works in Japan, but I'm thinking Sensei could be at least 30? Not sure.
Also am I understanding this right? Sensei misinterpreted Ebihara's request and gave her a special treatment she normally wouldn't give anyone else? Like, maybe there was some attraction/chemistry involved there? In the end though this is a one shot so we won't see any more of these characters.
I know this comment is old as hell (And maybe someone answered already), but when Daphie asks for "extra", Sensei thinks she's asking for "sexual services". In massage parlors you ask for an 'extra' when requesting a Handjob and the like. Most massage therapists will know this lingo even if they don't offer the service, because clients will ask them regardless.