In the light novel, Ayanokoji is clearly the more intelligent one. He has a unique ability to analyze situations and people's motives deeply. Ryuen often falls into Ayanokoji's traps because he doesn't fully understand Ayanokoji's true nature. Ayanokoji can anticipate Ryuen's moves and counter them effectively, while Ryuen struggles to keep up with Ayanokoji's complex thinking.
Leo would likely take charge immediately. He'd assess the situation and start giving orders on how to help Mikey. He'd be calm on the outside but worried on the inside.
Leo would probably take charge immediately. He'd be focused on getting Mikey to safety and finding a way to treat his injuries. He might be blaming himself a bit for not being there to protect Mikey better.
Mikey might be a character created to tell a story about Pop Rocks. He could be a fictional child used to illustrate the appeal or novelty of these candies. For example, he could be a curious and adventurous little boy who wasn't afraid to try new things, like Pop Rocks, which were quite different from other candies at the time.
I don't know for sure. The ending of such a manga can be quite unpredictable and might not have been revealed yet. You could try discussing it with other fans to get their speculations.
April and Casey might also be part of this fanfiction. April could use her reporting skills to try and figure out what's going on with Mikey's mutation, and Casey would be ready to fight any new threats that come along because of Mikey's changed state. Also, Splinter, as their sensei, would be guiding them all through this difficult time, providing wisdom and training to help Mikey control his new powers if he has any.