Hi, thanks for taking your time to write the review.
The manual is actually included with the game, it's the GAME.html file inside the archive (or game installation directory). You can also view it online. I do want to integrate it into the game itself eventually, as it should be. Sorry about that.
You're not alone with the complaints about visibility and overtuned difficulty. We're mostly focused on the extra stage for the upcoming v1.5 update right now, but those are on our radar as well. On the other hand, I'm curious about which patterns you thought were too easy.
The cast of bosses is kind of a mess, I agree. This is mostly due to the game's development having been started a really long time ago, when we were still in high school. The bosses were mostly chosen based on the lead dev's favoritism and story cohesion was, at best, a secondary concern. The game's story has actually been completely rewritten 2 times since then, by two different people, and both tried their best to retrofit the existing cast into the story. So this one isn't getting fixed, unless we make a Taisei 2 eventually. But at least Scuttle is going to play a role in the upcoming Extra stage.
Thanks for playing, your feedback is received. Hope you'll give the game another chance when 1.5 is out.