At the start of the series, Ginji Kusanagi (草薙 銀次,Kusanagi Ginji?), a high school student on the verge of making his professional debut as a boxer, is killed in a suspicious motorcycle accident on his way to his first date with Minako Sasebo (佐世保 美奈子,Sasebo Minako?), the girl of his dreams. An angel (who is depicted as a Buddhist monk with cherub wings and halo) tells Ginji that because of a celestial mistake, he can be reunited with Minako, but only if he lives out the natural lifespan of another animal, after which he will return to his human body. Remembering Minako's love for penguins, Ginji decides to be reincarnated as an Adelie Penguin, and he hatches from an egg in a Tokyo aquarium.
When Ginji reaches adolescence, he escapes from the aquarium with his penguin friends, only to discover he cannot swim. He washes up in the harbor, where he is discovered than Minako. She takes home and names him Gin-chan (at first thinking this to be an affectionate contraction of his own name, Ginji is crestfallen when Minako reveals that she has selected this name because, in her words, "You're such a cute little pengin! (ペンギン?, the Japanese pronunciation of "penguin")".
The series depicts Ginji's life with Minako, where he does his best to protect Minako from any man who tries to go out with her or simply "harm" her. Along the way, Mike and the other penguins from the aquarium help him once in a while and he meets fellow reincarnated humans.
Tuxedo Gin has been reviewed as having the sort of wacky premise and serious plotlines that make a good romantic comedy, unfortunately being weakened by mediocre characters. Tokihiko Matsuura's art has been praised for clean lines and clear layouts but criticized for its generic character designs.