The ship started sinking in Episode 15 when Hiro and Zero Two officially confessed their love for each other. It completely diminished following Episode 17, when Mitsuru acknowledged his feelings for Kokoro and consummated their relationship.

Does Mitsuru hate Hiro?

He was initially very cold, harsh and held disdain towards Hiro for supposedly breaking their promise of piloting FRANXX together. He would berate Hiro and at the same time try to surpass him, boasting that he has always been better at piloting a FRANXX at him, to the point he would even get cocky.

Who is in love with Hiro?

A thousand years later, Hiro and Zero Two's souls reincarnate as a pair of children that meet each other again and rekindle their romance.