I would think one possible bad fight would be about MKs sacrifice, and him possibly doing it again.
Mk is reckless with his own life, and he loves friends and family more then he could love himself, it's where his over protectivness stems from. (That and his self sacrificial nature is probably programmed into him by nature, fucking thanks nuwa. The THE ONE mother figure mk has and she had to be the one that fucks up a perfectly good child)
Nezha may be immortal but mk would still actually jump in front of a blade for him without hesitation.
Tw mentions of past and attempted self sacrifice
This works very well, afterall Nezha would do the exact same thing because he shares a similar mentality. You don’t just sacrifice yourself for your family without having some issues.
This would come to a head at a terrible time, mid battle with a demon! Mk and Nezha both struggling early on in their relationship, pre-therapy, wanting to protect the other while also bringing down the big bad. Nezha might take a blow that was meant for Mk, and Mk freaks.
He and Nezha get into it. Nezha isn’t that hurt, mostly bruised, but Mk is absolutely losing his mind over the fact that his beloved just got hurt because of him.
Then you have Nezha who is trying to talk to his bf, but mk won’t listen, and they progressively get louder and louder. Until it reaches a point where Mk and Nezha are screaming at eachother in the middle of the battle field, and the fighting just… stops, because nobody has seen either of them get like this. The demon akwardly apologies to the others and leaves because damn this is awkward.
But the two idiots don’t notice, they just keep up the screaming match. Until Nezha has enough, and tells Mk in no uncertain terms that this shit isn’t going to work. He’s a celestial warrior, he can hold his own, and he doesn’t need to be coddled. Mk tries argues that he just wants to protect Nezha, but Nezha stands firm.
They don’t talk for a month.
Nezha is miserable during that time, and Jing teaches him the wonders of growing your sorrows in (strawberry) ice cream and crying into the pillows.
Mk in the other hand is left to think, and with some encouragement form ye others, decides to seek therapy with Sandy. It’s not easy, and the whole month without Nezha is agonizing, but Mk is determined to improve himself before he asks Nezha out again.
After a month, Nezha’s absence was strong enough to motivate Mk to reach out. Nezha was hesitant, but accepted a simple picnic date “to talk”.
It was by far, the most sweetest thing. Picknic basket full of all of Nezha’s favorites, a pretty strawberry themed blanket, and quiet spot outside the city where no one could see them.
They chatted for a bit, akwardly feeling things out, until Mk comes out and apologizes to Nezha for all the hovering. He akwardly explains that he just didn’t want Nezha to get hurt, and that he never saw the Prince as incompetent. That seeing Nezha hurt, even if a bit, was like lighting a fire. But he also apologies for overstepping boundaries, and acknowledges that he is working on the problem.
Nezha himself apologizes as well, aware that he had similar reactions in the past to Mk taking blows for him. He also apologizes for causing such a big blow out about it in public instead of privately, but Mk insisted it was fine, and that it was the wake up call he needed.
Nezha def cries when Mk asked if he’d still be his precious strawberry, and Mk nearly cried when Nezha agreed.
This isn’t the last time, but it’s def a big step in their relationship.