I think i know what you're looking for with the musou attacks. Getting 100 enemies in one shot is actually pretty achievable once you understand how the war god rage system works (this is basically your ultimate power mode that changes everything).

The key is building up your musou gauge through regular combat first, because more hits means faster charging. When you've got a full gauge, watch for those dense enemy clusters - this is where the magic happens because musou attacks have this amazing radius that scales with how many targets you hit.

Your best bet is triggering war god rage when you're surrounded (you'll be invincible during this, which is pretty handy), then unleashing that true musou attack right in the middle of the crowd. The damage spreads outward in this devastating wave, and if you've upgraded to ultimate musou, it's even more impressive.

Something that's really interesting - you can actually chain these attacks together with your companions. While your musou is cooling down, swap to a companion and use theirs (they each have their own gauge), which keeps the momentum going. This works because the enemy ai tends to cluster around whoever's active.

Just remember, timing is everything here. Wait until you see those really dense groups forming around objectives or spawn points, and make sure you're positioned right in the center before triggering (this maximizes your hit count). And here's something neat - hitting more enemies actually fills your gauge faster, so you can get back to those big attacks more quickly.

Stay aggressive when building your gauge, but be smart about when you unleash that true musou - you want maximum impact for your effort.