I am so positively surpeised at how down to earth and straight forward everyone in this manga is and how it successfully plays with the usual manga tropes.
MC is actually realising he is in love and wants to tell her right away.
Lil sis sees something wrong with his girl (which is def true) and just says she does not like her.
BFF gets MC to spit out his worries right away instead of being shy or taking 5 chapters brooding/filler.
BFF promises to help AND ACTUALLY HELPS, but thinks the sis is a brocon, which is what all the readers have been thinking, too.
Sis just kinda also senses the ghost, who will most likely kill the MC if he ever hurts or breaks up with the girl. So sis just wants to protect her bro, AND THE MC ACTUALLY UNDERSTANDS THAT instead of crying 20 chapters about how much of a bitch his sister is for not approving of their relationship.
For real though, the girl and the ghost are dangerous: Imagine you date the girl and the ghost just does not like ypu anymore, cause she got bored of you. She can make your love life living hell..