Not sure if this even merits a submission really but figured I'd mention it anyway.
I recently watched the anime film Drifting Home on Netflix.
The two main characters are Natsume and Kosuke. Neither of them are blood related to each other, but due to Nastume's fractured home life, she comes to live with Kosuke's family at a young age and she's essentially raised as part of the family. She mentions that she looks at Kosuke's grandfather as her father figure, and beyond just being best friends it is frequently mentioned that the pair are basically siblings.
However, it's made very clear throughout the film that they both want to be more than "siblings", and by the end- while nothing is ever outright stated- they are obviously going to end up together.
(This point is made even further evident as there is another character who is actively trying to get with Kosuke romantically, but his attention is only ever on Natsume)
Nice find, Anon. Thanks for sharing!