In Volume 0, Koinzell's Establishing Character Moment where he slaughters a mass of Black Wing Militia with his implanted blades, then proceeds to curb-stomp their leader without breaking a sweat. All this whilst he was still recovering from injuries sustained by falling off a cliff.
Smug Snake Lacheb is about to have Altea's entire bar arrested and executed for smuggling. Cue Koinzell managing to take out his entire contingent of guards. How? By cutting loose the massive ornamental boat hanging from the ceiling, then riding it all the way down to the ground, crushing most of Lacheb's bodyguards in one fell swoop.
Pago's much-deserved Karmic Death at the hands of Geranpen, Ato, Koinzell and Vid.
The entire fight between Schtemwolech and Koinzell. It's the closest fight in the manga up until that point against an enemy Koinzell can't simply steamroll over. Plus it culminates in the first and so far only appearance of Koinzell's One-Winged Angel form.
Ifekes vs Koinzell (which started with him riding in atop a dragon) was so awesome that even the In-Universe audience was drawn into it. When it ended due to the instigator blowing the side of the arena up, they actually rebelled.