I'm not sure if there is an official fanfic with such a plot. Fanfics cover a wide range of themes, but this kind of plot might be considered quite extreme and not in line with the original tone of many series. However, there could be some out there in the vast world of fan - created content.
Well, one interesting plot could be Clary slowly regaining her memories through a series of magical encounters. Maybe she finds an old object that triggers flashes of her past. Another could be that her friends play a crucial role in helping her get her memories back, like they take her to special places related to her past. And a third possibility is that there's some sort of enemy who is trying to stop her from getting her memories back, which adds a lot of suspense to the story.
Well, one consequence could be a major shift in their relationship. They would have to deal with the responsibilities of having a child, which might include changes in their living situations, education (if applicable), and social relationships. Their families might also get involved, adding more complexity to the story.
In the comics, Vision regains his memories through a series of events and interactions that trigger his internal processes and reconnect him to his past.
Clary is the central figure. Valentine might also be involved in some fanfictions, either as an obstacle trying to prevent Clary from getting her memories back because he doesn't want her to discover certain secrets, or in a more complex way where his past actions are somehow related to the loss of her memories in the first place. And of course, the Lightwood family members are likely to be involved, given their importance in Clary's life and the Shadowhunter community.
One common theme is growth. Both characters are often shown to grow as individuals and in their relationship with each other. For example, Mori Jin might learn more about patience from Mira, and Mira could learn about taking risks from Mori Jin.
One idea could be to cross Mori Jin with a character from a different anime like Naruto. Mori Jin could end up in the Naruto world and have to deal with different jutsus and the ninja way. He might even teach some of the ninjas his own martial arts skills.
Hermione could be the one. With her vast knowledge of the wizarding laws and her sharp intellect, she might dig up some old regulations that prove Harry's right to his money. She would then fight tooth and nail in the wizarding courts or against the goblins at Gringotts to get his money back.
Maybe he discovers some legal loophole in the wizarding world's financial system that allows him to reclaim his inheritance. For example, if there was some improper handling of his family's vault by the goblins at Gringotts, he could use that as a basis to demand his money back.
Light Yagami from Death Note. It would be a contrast in characters. Mori Jin could find himself in the world of the Death Note and try to stop Light's plans, or they could form an unlikely alliance where Mori Jin tries to change Light's view on justice while also dealing with the power of the Death Note.