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Tear Jerker: X-Men: Evolution
In "Shadowed Past", Professor X visits Mystique to discuss recent events involving her son Kurt and asks her, "Was It Really Worth It?" The episode ends with Mystique watching a mother hug her daughter goodbye as she drops her off at school.
In a flashback (which Rogue first misinterprets as a dream) it's shown that unlike most of her other incarnations, she accidentally lost Kurt after trying to find a way to treat his mutation.
In the episode that introduced X-23, her Back Story was virtually nothing but this. Then we have her breaking down during her conversation with Wolverine...
To solidify this, just look at the HYDRA employee who tells Wolverine about her and her involvement in X-23's creation and life. Wolverine is outraged and demands to know how this woman sleeps at night. Her response: "I don't."
During Angel's introductory episode, an apartment building is burning down on Christmas and a teenage girl is desperately trying to get inside and save her mother, crying and screaming since the lady in a wheelchair and cannot escape on her own. In a Crowning Moment of Heartwarming, Angel saves the lady and places her gently on a nearby bench, and soon she's reunited with her daughter.
"Been a long time, Cap, but I'm still fightin' the good fight. Today we had a victory... for you. You gotta know we'll find that cure; I promise you that. Because you and me... you and me, we made a great team. Yeah... I'll be here when you get out."