Alys and Rune
I really think that there was something between them. I also see them as a romantic couple, but it's a special love. Well, here it goes:
1- I think that Alys loves Rune. But I don't mean that "brother-sister" love. I think that she loves him, but that she wasn't counting the days to see him or thinking all day about him.
2- When the party meets Rune for the first time, Alys blushes when he invites himself to go to Tonoe with them and accepts his "invitation". Ok, you can blush because of lots of things, not only because the guy you love asks you something or invites himself to go somewhere with you, but thinking that way, my theory may seem invalid. :)
3- In the same scene, Rune says "I won't get in anyone's way", and Alys says: "You already have". That can mean that she has something with him!! Somehow, he hurted her in the past and now he appears again! That can also mean that her life could have been very different if he hadn't appeared before! His appearance in Alys' life changed her for ever...
4- Then, after arriving to Tonoe and almost killing Grandfather Dorin, Rune leaves (buahhhhhh!!!! It's not fair!!!!!).He tries to calm Alys down (sweet Rune!). And his goodbye to Alys is so... sad. (Rune, I'm gonna kill you!!). It seemed (to me, at least) that it was like a different conversation, that there was a different atmosphere between them. (Now that I think of that scene, how did Dorin get Alys's measurements?) :)
5- When he learns the news about Alys and the Black Energy Wave (well, first of all he feels that something has happened to her), he says "Such a thing happened... Alys...". You would tell "What's the matter in that sentence?" "Don't you notice?", I would say, "I'm sure he said it in a sadly voice"... Well, that's the point. Or he felt the same (or something similar) for Alys, or he considered her a great friend. Now, it was pretty stupid of you, Mr. Walsh, to decide to pick the Psycho-Wand first. (personal opinion; now that I mention it, I've always wondered why he decided to get the Wand first...)
6- When Alys is dying, she calls him and he answers "I'm here... I'm right here... Alys" (that scene almost makes me cry, oh, stop showing my feelings, I'm showing a theory, not telling everybody which part makes me cry or not) =P Well, that scene seems vey romantic, don't you think? And then she asks him to help Chaz, and he says "Leave it to me..." (Oh, sweet, sweet Rune). The question is: Why did she ask Rune to help him and not to the others? Maybe because she trusted in Rune... or because she loved him.
7- The night after her death (or after her funeral), Rune tells Chaz that she wasn't fighting for money. It isn't very relevant here, but that shows that he knew her well. (I don't know why I listed this, maybe later I'll know) =)
8- After that conversation with Chaz, he looks at the stars. (Another thing I've always wondered; maybe he was asking the Light why all the things he loved disappear tragically? or why his life was too difficult?)
Maybe I hadn't been so convincing, but I see them as a couple. But, as I said before, it's a special love. I can't think of an Alys crying all day because her "little Rune" wasn't by her side. Or a Rune desperate because his "honey" died. I see Alys as she had tried to forget him, but when she saw him again... all those good moments they had spent together some years ago returned to her... But she continued her life as nothing. And I see Rune as he loved her (maybe), but he never showed his feelings. And after her death (and the game), he still loves her (as a woman, as a friend, as whatever, but he loves her), but he isn't of the ones that may cry all day. I see him as someone capable of remember the good and the bad moments at her side; and remembering every so often.
Well, with this theory you can see how much I like Alys and Rune. In fact, they are my favourite PS4 characters (both in the first place) :)