This is a very pleasant game! I appreciate it featuring some creatures that we might otherwise not see very much or very front and center. There's also a good target audience in mind.
As somebody without much experience with retro Sega games, I would be curious about some minigames that use the spirit animals to some more extent. The... inspiration game had racing and karate, for example.
Edit: With that said, the cross-game compatibility was an amazing detail! It's extremely rare that I see something like that!
The music was also nice, although I did find the sound effects slightly loud in comparison.
Otherwise, it's a very cool concept that has a lot of room to put whatever else might come to mind! ^.^