I played this without knowing any Japanese, what this game is could be described as a "virtual fish tank" game, this is a niche genre typically not localised, I've seen other examples of it.
Another way to describe this game would be similar to the chao garden in Sonic adventure (2) where you raise a creature, and maybe watch it compete in a race. In other words it is a "virtual pet" game only less interactive.

Visually it's a mixture of cel-shaded and very colorful abstract environments. It's not very polished looking using simple geometry and sparse areas but the way it looks was striking to me.

Most of the game is just watching this Mutsu creature randomly wander around as it finds collectibles and talks to other strange abstract creatures.
You can only start with one area out of 12, so when playing the actual game you can't really interact, pushing directions seems to indicate you are directing the character but for me it always ignored it, you can talk to it with typed messages or give basic commands in japanese but these don't seem to do much.

The character randomly finds items you can select to make it transform what you get is random every time, I think they also improve it's attributes in some way, it seems to have a mood status too.

Each of the 12 areas has an objective, I couldn't really figure out what they were but when waiting around long enough the character would eventually wander to whatever it was supposed to and activate these events, once this happens other levels open up.

2 of these are completely non interactive race levels where you watch Mutsu navigate them, again just like Chao Races in Sonic Adventure, I lost once but came back later and won both but I'm not sure what changed to cause it to swim faster.

The nice thing about these areas is they all look distinct and unique from each other, it more or less the main feature of the game, the colors are vibrant sometimes neon, one area was mostly pastel, but I appreciate the creative and otherworldly look some of them had.
It took forever to complete these levels since the creature randomly explores them sometimes looping around or talking to the same npc over and over again, I feel like I'm missing something but I still have no idea.
once you "complete" all 12 you can reach the credits.
I never figured out how to save and left the game on to complete it. There is no fail state, the game seems to be intended to be as stress free as possible.

The entire point of the game it to watch it, like you might a fish tank, it's not really about playing it. This is something you could leave playing in the background while doing something else.
It was nice just looking at the vibrant and trippy worlds as nice catchy music was playing, the game has a specific mood and atmosphere.
I think it does this aspect well enough.
I really enjoyed the soundtrack too, it's varied and music tracks are unusually long to not get repetitive as you may spend hours in each area, it was one reason that I went out of my way to get it.

I have mixed feeling on this, it's not fun to play, but it has really good atmosphere and it's a unique experience.

So if you want something strange to play in the background or want something else to relax with this might be worth looking into.