Wow, that ending hit me like a brick. When I first saw that scene I got so pissed off that I decided I'd better rewatch it before writing my thoughts, and I'm glad I did. Lara is not quite as heartless and aloof as I remembered, but it's still a very painful watch.
Judging by Lara's text messages it seems that her destination is some 4 hours traveling by train train away, so not around the corner. So where is she going? How will she get by? She has no money, no skills and no experience. Maybe someone scouted her to become a model? Or an idol? I mean, she is a mermaid after all.
That whole scene comes across to me as the last stage of a relationship, with one party wanting to keep trying, while the other just feels the need to move on. Mari's question why Lara had to leave feels like last-ditch effort to make her reconsider, but Mari quickly seems realize it's no use anymore. She may have asked numerous times, never getting a real answer, and right now they're standing on that platform, waiting for the train that will finally take Lara far away.
Poor, poor Mari. First she loses her mother, then her beloved Grace, and now the girl who said she'd live with her is breaking her promise big time. Mari loses her mother's keepsake, and literally dies for Lara, and mere months later it's rendered completely meaningless. I felt so sorry when she teared up, and the least Lara could have done is give her a hug, but she doesn't. It's just so heartbreaking.
Ah well. So here we have yet another yuri(-ish) show where the makers swerve away from giving two girls any type of romantic resolution, to the point of having a last scene that pretty much ruin the rest of the show. Good job, everybody!