Isn't this the "winning CG" of Lucy's route, where she and Takaki got brainwashed by the aliens to forget that she ever was an alien, then brainwashed a couple to believe Lucy was their "daughter"?
sort of the ending is after leaving earth, ruko later shows up at his home and she believes her name is lucy maria. so when taka calls her ruko she says her name is lucy and she is from california. so then he says did you forget about all the memories they shared together and she says of course not, she remembers them all. apparently she was brainwashed so she could return and live a normal life. ruko and lucy both start with the letter R in JP. i dont know how to add spoiler tags to this.