I was watching the Sega Ages: Space Harrier trailer for Switch and I discovered that there's an extra track related to Haya Oh, which was previously available as a extra boss in the Master System, Famicom, Sharp X68000 and Game Gear versions of the game. This track was previously featured in 3D Space Harrier for Nintendo 3DS, since where the Switch version is based on.
The remix starts a 1:01:
https://www.youtube.com/watch?v=EyGalYYzWmw
And the full version, recorded from a 3DS:
https://www.youtube.com/watch?v=uWk2rp_RnGc (very low volume btw)
To fight against Haya Oh, the player needs to either reach on Stage 18 without using continues or, with Stage Select, clear Stage 18 without losing a life. So, Haya Oh will appear and his respective theme will play.
The method for the Switch re-release probably be the same.