You must either watch 1995 hit anime Neon Genesis Evangelion, or live the rest of your life not understanding this joke. I’m sorry, those are your only options.

It’s a joke about the animated film Ratatouille that uses a reference to Neon Genesis Evangelion. Ratatouille is a movie where a rat pilots a human by hiding under his chef hat and pulling on his hair, in order to fulfill their mutual dream of being an expert chef. Evangelion = humans pilot battle mechs and cry a lot.