This was almost a month ago now, but my last big 1cc was Espgaluda II: https://www.youtube.com/watch?v=MraBCPsbHpY
That's probably been my hardest clear thus far, but I felt that it wasn't too much harder than Futari Original? For pure survival, a lot of the bosses just come down to resource management with Asagi; learning a route to reach each boss with 500 gems, and then spending the gems to skip risky patterns instead of burning through bombs.
Fun game though. I love how they doubled down on the horizontal bullets from the first Espgaluda's final boss. Half the bosses in this game end with some kind of slow-moving horizontal pattern.
No idea if the final boss's final pattern is beatable with no miss/no bomb with other characters. Feels like you have to be in kakusei for it, and you'll die once your gems run out. That's probably my only real complaint. In comparison, it was really fun to do a perfect clear (no kakusei) in practice mode for the final boss of the first Espgaluda, even though I'd never risk it in a real run.