I have finally consumed Deltarune for the first time, up to chapter 5, not including Chapter 5's weird route stuff. (Haven't seen anything of Undertale.) So, some rapidfire thoughts.
Berdly reads as aroace and doesn't know it. He is desperately lonely, autistic and doing a bad job at friendships. If he gave up trying to be alloromantic and stopped pursuing romance because that's what highschoolers do, he would be much happier, and a lot more tolerable to those around him. Even if he is not aroace, he is not ready for romance. He's just lonely and needs to stop ruining his friendships.
Susie and Noelle are gay for each other. Bratty and Catty are gay for each other. Kris likes Susie romantically (according to chapter 5). Ralsei is secretly a closeted trans woman (according to chapter 5). I consider these things canon, from what I can tell based on dialogue. I mean, Susie and Noelle are as obvious as can be.
My personal feelings for main five ships are: Kris/Susie with Ralsei as their queer platonic third (at least with Kris) because Ralsei and Asriel look so similar. Berdly stays out of anything romantic or queer platonic (bird boy is not ready). Noelle can kiss Susie, or not. I can't make myself care about Noelle/Susie very much for reasons outside the game.
Spamtenna, as they are in canon, will always be toxic. Spamton and Tenna have a lot of similar issues, a lot of issues in general, and should be in therapy, but there don't seem to be any therapists anywhere in town to steal a ... I don't know, a clipboard from to help the Darkners. They bring out the worst in each other and struggle with accountability, no matter how hung up they are with each other.
That being said, I have an alternative I like a lot. And that's Jackenstein x Tenna. I think Tenna having someone who's sweet and spotlight averse would be far better for him than Spamton. With Spamton, their ambitions carry them away, but with Jackenstein, Tenna can theoretically be a little more grounded. Overall, I think, despite Tenna continuing to have issues, being with someone wildly different than himself, Spamton, or the Mikes would be better for him.
A big theme of (Kris's character and by extension,) Tenna's character is letting go of people. Tenna hurts so much over the Asgore/Toriel divorce, much like Kris. He wants to bring them back together and fix things. He feels that former love should always be brought back together without regard to the issues that split them up in the first place. That's why he wants Asgore and Asriel back. That's why he wants Lanino and Elnina to get back together. That's why he pines over Spamton.
But while Lanino and Elnina are able to talk over their issues, it's only after a couple of changes in their dynamics and honesty that they're able to come back together, and their mistake could be rectified by simply remembering to value each other, Spamton and Tenna more closely resemble Asgore and Toriel, who have much deeper issues.
Spamton and Tenna aren't willing to be honest, and with Spamton's 'relationships based on deals and scamming', trust issues, and bitterness about the past and Tenna's dependency on living in the past, they won't be able to change the issues that broke them. In fact, Tenna's dependency on the past can only be fixed by letting go of Spamton. Asgore can't fix his relationships by pursuing Toriel when she doesn't want him and refusing to admit fault. Similarly, Tenna's can't be fixed by pursuing Spamton without addressing and changing his issues in the relationship. Fundamentally, based on their characterization, there is simply no way for these two to be willing to change without some massive shift from outside the relationship. Something needs to change and these two refuse to on their own.
Meanwhile, Jackenstein being an anxious person, I think having a more extroverted boyfriend could be good for him. He expects to be rejected for his appearance, so having someone like Tenna be interested in him can do wonders for his self esteem. Scary dog privileges, you know? 'He asked for no pickles.'
Mettaton might also work, but I know nothing about him, so ... I'll go for my pumpkin sweetheart x TV crashout pairing. :)
There should be more family focused, Kris and Tenna fics, because they're very important to me.
Jevil and Spamton should be roommates who hate each other.
Queen and Tenna should be friends. Queen gives terrible love advice, about 70% of the time, and it's hard to tell what kind you're getting.
I hate Rouxls. He doesn't spend enough time with his kid and he was a terrible partner. Didn't even learn their names or what they were, just wanted to use them. He's a creep.
And ... with that, I think I've got everything. For now, at least.
@olliethescribe you should get to see this.