Ah! My Goddess Avatars

The manga tells the story of college freshman Keiichi Morisato, who, because of his pure heart, has been chosen by Yggdrasil, Heaven's computer system, to receive a single wish. The angelic "goddess" Belldandy is sent down to Earth to ask for his wish, and tells him that he can potentially wish for anything that he wants, from becoming a billionaire to destroying the world in an instant. First, Keiichi thinks that this entire meeting is a prank being played by his senpais, but during their short meeting, he soon realizes that she's the only person who truly understands and appreciates him. Being enchanted by her, Keiichi wishes if her offer is truly valid, for someone like Belldandy to stay with him forever (not knowing what he wished for, was going to become). The manga/anime follows their relationship as they become closer to each other.
Being a mechanical otaku himself, Fujishima frequently bases whole chapters, or even story arcs, around mechanics, focusing especially on motorcycle mechanics. Most notably, readers discover that Keiichi Morisato is a member of his college's motor vehicle club, which is always under threat of being put out of commission by a rival motor club. There are also several story arcs related to racing found earlier in the manga; the concept of racing is also a significant plot device in each of the anime canons. Both Keiichi and Belldandy are exceptionally gifted at racing (Keiichi because of natural ability and Belldandy because of her ability to "talk" with the machines). Most of the other main characters have exhibited some degree of skill in racing and/or mechanics, making the idea of mechanics a significant device for character development and growth.