So, we've only seen the first three years so far, and still have 14 years to go, and I wonder where this is gonna go. Possible endings for the Elf:
1. Ojisan eventually recognizes her feelings, falls for her, possibly marrying her, but something happens and she dies, and so he erased memories of their relationship.
2. Elf finds out he keeps erasing parts of his memory and the magically suppressing his feelings, which made it impossible for him to ever fully recognizes her feelings for him, and it forces her to go off into the deep end , becoming basically yandere, and starts to legitimately try to kill/cripple him so she can force him to recognize her feelings. This further fuels his need to get back to the real world to escape the Elf. He maybe erases memory of her going off the deep end when he gets home. Eventually SHE FOLLOWS HIM TO EARTH.
3. Elf finds out he keeps erasing parts of his memory and the magically suppressing his feelings, which made it impossible for him to ever fully recognizes her feelings for him, and she actually gives up on him, since he's damaged himself too much. Before he gets back, she tells him all this before leaving to the Elf lands for good (Bonus points, this is when she's actually the nicest to him), and Ojisan, realizing that she liked him this whole time, and accidentally played with her feelings so much that it legitimately hurt her and made her recede from the human world, reaches a painful breaking point and erases his memory of that and returns to our world.
4. She stays how she is and only says something about how she actually feel once Ojisan is headed back to Japan, but because of the magic or circumstances, he misses it and never knows how she feels.
Endings for Mabel:
1. She gets worse and more of a homeless Need to the point where she's redeemable by the time Ojisan leaves. Possibly becoming more dependent on him as time goes on.