Happy to hear you like the game!
There is no plan for further routes to be released at the moment. But there will probably be an epilogue/side story released later on. And Tsurugi actually has a dedicated chapter in the recently released light novel: https://raikon-kitsune.itch.io/melodies-of-yesterday-and-tomorrow
It's a short sequel story and a bit of a teaser of how his story continues ;D