Finana has made clear she has an interest in Selen at some points, particularily during Millie's birthday stream where she was quite drunk. There is not much going on between them, though.
Strange as it may seem, I have a feeling Caitlyn is the more forward one in Arcane. She had far more moments of seeking out Vi. I hope to see this more strongly expressed in season 2.
Ocean law was a meme born from Selen stealing stuff from Minecraft. The pairing is due to their collabs as mentioned by Licentious Lantern and Norainhere.
Finana has made clear she has an interest in Selen at some points, particularily during Millie's birthday stream where she was quite drunk. There is not much going on between them, though.
It is true that they don't seem to be that close. I think Rosemi and Selen are much closer with each other. Also, Finana was drunk during that stream and she said a lot of crazy shit. Millie, too, who was the one who said she would marry Selen.
@Sasackie: The author stated that they are Amber&Eula on his twitter, and even if it's true they have a somewhat similar hairstyle it is what it is, it's hot nonetheless. :)