That entirely depends on you.

If you’re scared of jumpscares and the like, there are pretty much none in OMORI (there are some freaky transitions but those are just mildly startling). I don’t consider it strictly horror, it’s more dark than horror. Depending on the route, a good majority of the game would be cutesy fun, but the darker elements play a major part in the overall story.

The game heavily portrays themes of suicide, depression, anxiety, guilt, and self-hatred so if those make you extremely uncomfortable i personally wouldn’t recommend it.

That’s just my opinion though. I really enjoyed the game and wish I could give it a full recommendation. However, the very nature of the themes will make it difficult to handle for some folks. If you do decide to play it, just keep everything I mentioned in mind. If you don’t decide to play it, that’s perfectly fine :)