Wanna know
Hey if you still wanna know I did actually end up finding it. Just now. After spending like, 4-5h scrolling thru different genre configurations and typing different keywords into mangago's search bar. Turns out it's glitched out and shows something completely different, and doesn't pop out the name if you type it in. Luckily I remembered the plot pretty accurately so ggling the right sentence got me the results pretty quickly. Kinda regret not turning to ggl first, but I thought no way will anything pop out at first, ah, to smack past me over the head. Here's the link
http://www.mangago.zone/read-manga/a_lollipop_or_a_bullet/?SOkD
You're amazing for hitting me up after you found it not a lot of ppl do that so thank you. The story intrigued me because it kinda reminded me of a great manga i read not too long ago, I'll let you discover it, it's called My Broken Mariko
A girl transfers to a school on an island. She claims to be a mermaid and says that on -date- she'll go back to the sea. Befriends another girl and some things happen. They plan to run away cause the transfer's dad is totally messed up, the island girl goes to her place at night and witnesses??? her dad cutting the transfer girl into pieces and putting her in a suitcase, it's the date she kept saying she'll go back to the sea on.
So these are the things I def rmmbr, the transfer girl had I think short? but definitely black hair. Nothing else.