Eugh. I give this one 5.5/10, rounded up.
I can tell the author just hasn't put 'realism' in his list of priorities, at all.
I'm not asking a lot, just... Look, if you have super speed, you're going to forget that you have super speed exactly once, cause a small disaster, and then you train until you have unconscious mastery. Just because you, the author, invented the character 5 minutes ago, doesn't mean they have 5 minutes of experience using their own power. You need to simulate that shit in your head.
And there are a bunch of similar misses, like the would-be man-eating plant who went from threat to pet with zero inertia.
The author is just playing around with his character and setting, inventing character traits at the spur of the moment, bumping them into each-other, and seeing what happens.
You do that in, like, the conceptualization phase.
This manga is half-baked.