The best way I'd describe this game is "What if the snake in Snake was a sumotori, chasing rice balls instead of dots". Since your sumotori does not grow in size or in length, but instead he gains speed for every rice ball eaten, this game manages to be both easier and harder than Snake.
The difficulty of this game is entirely dependent on RNG and rice ball placement, however. Even at elevated speeds, as long as they spawn a decent distance away from the walls, it's comically easy.
But one bad spawn, and you're probably going to go too fast to take the rice ball without hitting the wall - sometime they appear to spawn INSIDE the wall, making losing a life inevitable
Suggestions: Replace the 'gain speed' effect by a 'gain size' effect and make each level end after a set amount of rice balls; each successive level will instead give you a higher starting speed. Perhaps a wider playing field (or a smaller starting size!), or walls/hazards for higher levels.
As it stands, it's functional, but it could become more interesting with just a little more effort.