If you were hoping that Ninjala was going to offer some sort of singleplayer content, you're in luck. That is indeed on the way, but you'll have to pay for it.
It seems GungHo will be offering singleplayer DLC on launch day for Ninjala, and it's going to be priced at $10. We don't know the full details of what to expect from this singleplayer mode, but we should see some content in the near future. Ninjala is set to launch on June 24th, 2020.
While we wait for more details on the singleplayer content and the game's launch in general, you can check out a fresh batch of screens here.