Hitoribocchi no Chikyuu Shinryaku
<PERSON> is high school student who lives with his grandfather and helps him with his coffee shop, he has twin brother who's sick and stays at the hospital. At the entrance ceremony he meets strange girl wearing a mask, she claims 10 years ago she came to earth and saved his life by giving heart to him and she tries to reclaim it, but the heart completely assimilated with the boy, she. offer to be friends and take over the planet. Of course the boy refuses and leaves to help his grandfather at the coffee shop, but soon is attacked by another alien, the strange girl shows again and says that she will help if he will become her friend and help her take over the world.
Later in the story we found that she lives in abandoned tram. The earth is isolated planet and only with keys that are on earth will help to access full invasion. Only special individuals can go to earth because it's "locked". 322
So the girl and the boy defend the planet from other aliens and also search for the keys.
I don't want to spoil the story anymore because the story is amazing one of the best sci-fi I ever read and the art style is amazing shame that it is not so popular.
some visual proofs the Tram she lives in
Ferris wheel scene story has multiple scenes with ferry wheel, It really sets the mood with the magical/otherworldly nature of this manga another cover
Sorry I got here searching for this specific manga so I don't really know proper rules and I'm not native English speaker, so if there's mistakes or need to add something comment. And I hope this helps. 100% sure that it is this manga he is talking about and the events he describes are a lot further in the manga. Manga is still ongoing.
Searched for hours, but finally found it. Google search is pretty useless because it searches what is popular and based on cookies, so to find it what I did was specify manga website and then search by description. Only then it gives normal results. 322