As a plot point, itxs used to build angst and yearning from the ML pov. Like there's this shallow belief that men can't develop feelings for someone unless it's a trigger/core memory from childhood. But having it for all of them is definitely lazy and bad writing. They were kids in various levels of hurt and they all latched onto the one person in their childhood who "saved" them.

while everyone is annoyed about the romance i'm annoyed about her being sis con, i like more selfish mc's, after few chapter forgot about thay annoying sister and became annoyed with mc for being too clueless, i mean there is a limit for someone's cluelessness, it was cute at only at first, and she meet most of the as a child and saved them even before she got her memories back!!!! she was supposed to be a villainess in the original story how is that even possible!
and i hate it when they meet as kids God such waste of time and nerves