You know, HUG would probably be a valid "battle" option if this were a crossover with Undertale rather than OMORI. I can only imagine how Frisk vs Nightmare would go...
Though, honestly, I could see Undertale x Mouryou no Nie, considering their plot descriptions start off practically identical. Basically "long ago, humans and monsters coexisted, then a war broke out and the humans were victorious, and they sealed the monsters under a mountain."
Anyhow yeah, likely putting the next chapter up tomorrow morning. I actually had a decent conversation with a reader in the comments of the first chapter. Likely not a hardcore Inyouchuu fan, since he (?) was rather nervously looking for confirmation that the fic wasn't going to get too explicit, but clearly familiar enough to be able to engage with the story. Regardless, I think it was pretty cool to have some correspondence on it. Shard and KED have already faithfully left their marks too, Shard of course being the writer who put that one cheeky Inyouchuu reference in his own fic not long ago.
Chapter 2 will be digging into some Dream Team vs Nightmare battle gameplay mechanics (see illustration above) in which everyone has abilities they're shown to have in official media. Quite a long way to go before we reach the chapters I just finished... I will say, however, that Chapter 17 dares to delve into both psychological and tentacle-squirmy torture, and to be honest, I think it might just inch out DHTBoS in how graphic it gets. Obviously a far cry from literally anyone else who writes an Inyouchuu fic, but still, I'm milking that "mature audiences, non-explicit" rating for all it's worth.