Kazuki's very first (unofficial) fight while piloting Hartzenen, things where a bit shakey at first. But man, did he give that mech a Curb-Stomp Battle.
In "Illegal Guy", when Kazuki is forced to snap out of his Heroic BSOD to save Mitzuki. Even if she was just faking in order to give him something to snap him back to reality.
The obviouse reference to Evangelion in the episode "Intrigue". Mitzuki literally leaps into action at the docks, just like when Akane and her robot where first introduced.
When Kazuki and Hartzenen were caught by the "Original", and Kazuki went all bat-shit crazy on the thing, smashing it to pieces.
When Genbu first awakens in "Escape".
In the second to last episode, ZINV/Jinbu/Genbu can create a controlled blackhole. Not to mention his Light Hawk Wings.
During the series finale ZINV/Jinbu/Genbu is revealed to be Kazuki's Alternate Universe conterpart. Turns out he must be sacrificed to seal the rift between the worlds. The best/worst part comes when we find out that he's okay with it. It's okay because he gets better later.