One moment, and he'd transmigrated.
Bad news: it's Honkai Impact 3rd.
Good news: it's not Honkai Impact 3rd.
Luckily, he got a System.
[You took someone's place and became Otto's unattainable first love.]
[You died.]
"?"
[Achievement unlocked: Otto will regret losing me for the rest of his life.]
[You are beautiful. The immortal pats your head and ties your hair... to become husband and wife?]
[You died.]
"?"
[Achievement unlocked: The immortal will regret losing me for the rest of his life.]
[You were rescued by a saint of the Schariac Family...]
[You became Miss Sirin's imaginary friend...]
This System is a little strange...
(The blurb doesn't do it justice. Please check out the story itself.)