Beoryeojin Naui Choeaereul Wihayeo

What happens after the story ends with a “happily ever after”? When Hestia enters her favorite novel as a side character, she happily fangirls from the sidelines. Thinking she’ll return home when the story reaches its end, Hestia finds that the only thing awaiting her is the tragic death of her favorite character. Now miraculously restored to the day of the ending, Hestia decides that she’ll no longer spectate from the sidelines – instead, she’ll save her derelict favorite!
(Source: WEBTOONS)