Papa Mokou said:
If that's possible, then I think it would be wonderful if we could live together once more.

And in one fell swoop Shuga has given us something most versions of the story lack: A reason for Mokou to give a damn about the failed attempt at marriage. Reason enough to lead to her becoming a murderess as she eventually does.

Other possibilities existed. Such as Mouko being a psychotic daddy's girl who resented Kaguya merely for rejecting her wonderful father. As well as unfairly blaming Kaguya for the shame that befell her father and household when Kaguya publically denounced the treasure her brought her as a fake... nevermind that it WAS a fake.

Mouko wouldn't even need to be psychotic OR a daddy's girl to unfairly blame Kaguya for the shame and disgrace.

Further, Mokou's own official retelling of her past reveals that at least half of her endless vendetta against Kaguya is fueled by simple momentum. Or perhaps: It's not so much that vengeance is more important to her than anyting else, as it is the only thing she has LEFT to care about.

I'm pretty sure "Powerful, Crazy, and Bored" is pretty much the only valid reason for an eternal feud that continues on centuries after everyone else they ever cared about or were fighting over had died, although making Kaguya like Mokou a bit, and tempt her into being immortal with her to be her eternal rival/plaything is a decent, and fairly reasonable touch.

In fact, "they're Powerful, Crazy, and Bored" is pretty much the plot of 3/4ths of everything that happens in Gensokyo.

Red_Inugami said:
Other possibilities existed. Such as Mouko being a psychotic daddy's girl who resented Kaguya merely for rejecting her wonderful father. As well as unfairly blaming Kaguya for the shame that befell her father and household when Kaguya publically denounced the treasure her brought her as a fake... nevermind that it WAS a fake.

Mouko wouldn't even need to be psychotic OR a daddy's girl to unfairly blame Kaguya for the shame and disgrace.

Further, Mokou's own official retelling of her past reveals that at least half of her endless vendetta against Kaguya is fueled by simple momentum. Or perhaps: It's not so much that vengeance is more important to her than anyting else, as it is the only thing she has LEFT to care about.

I wouldn't call it an unfair denouncement. Mind you, Kaguya humiliated Fuhito when he proposed to her. And with an impossible request, no less. Kaguya bewitched countless people with her wiles, and Mokou got caught in the middle of it. This is what, initially, drove Mokou to get her revenge. After reacting by stealing the elixir of immortality, Mokou could no longer live like a normal human anymore. She was forced to travel as a wander for centuries. By the time in the events of IN, it seamed she gave up on feud altogether, and it was in fact Kaguya who dragged on the meaningless battle. I would say, Mokou is irritated at Kaguya for driving her to ruin her own life. She blames Kaguya for her sins, but she's somewhat in the right. She was only a child when this happened, after all.