I’d probably do ThunderIron with a post-Ragnarok Thor and an older more mature Tony having difficulty relating to the people around them and naturally turning to each other for companionship. Both of them have been responsible for the lives and wellbeing of thousands of people, have failed those people, and have struggled to be better as a consequence of that. The struggles of a king aren’t exactly relatable for most folks. Thor’s probably the more trusting of the two of them, so he’d make the approach. All of his gestures would just be these quiet requests for comfort, for acknowledgement, for friendship - like the scene of them meeting again in IM, Thor is a social guy who gets lonely easily. Tony’s ultimately a giver and wouldn’t be able to resist the opportunity to spoil someone - that’s how Tony practices self-care. Thor wants company and contact so badly.They always find themselves talking at night, drifting through the halls alone and wondering what they could have done better. Tony is usually angry when confronted with his anxieties, but he just can’t snap back at Thor, not when he’s got this whole…gentle giant thing going on. The fact that Thor respects him also makes him reluctant to be rude - respect is in such short supply for Tony these days. So instead he turns to talking in riddles and metaphor. Thor meets him line for line. They begin discussing philosophy when really what they are discussing is both of their struggles. They talk about literature when they are really trying to see if they’re both ok. They poke fun at themselves and their families and their old pains. They drink and watch the stars and murmur about their most epic adventures, trying to pretend it doesn’t make them sad. And then they find that huh, it actually doesn’t make them sad anymore. Because Thor’s old war stories bring a sparkle to Tony’s eyes. Tony’s party day tales make Thor laugh like he used to. They don’t need to be ashamed about the past around each other. And when they are anyway, they’re there for each other to build a better future. At this point, because I love Extremis Tony, I’d probably pull some grand symbolic stunt of Tony repeating his and Thor’s first meeting in the MCU - the suit being charged by Thor attacking him. Tony would be all, “Charge me up, Big Guy.” and it’s dangerous, it’s stupid, but Thor has seen the way the little sparks from his skin just sink right into Tony and make him glow. So he goes for it. And Tony is incandescent - lightning in human form. Without even thinking about it, Thor kisses him and they short out every single circuit in a five mile radius. Basically it’d be an old souls romance with making each other feel young again, but also “damn it all we need to take command of large numbers of people and the responsibility sucks, BUT it also looks REALLY GOOD on you”. Including Bucky would be such a shakeup because Bucky isn’t the leader type. He’s a huge caretaker and I have no idea how he’d handle two sad kings who are also big caretaker types without just up and murdering them. I could see some kind of platonic relationship forming with Thor because honestly idk if Bucky, loyalty incarnate, could handle two romantic relationships AND take care of himself at the same time. So maybe Thor and Tony fall in love, however the pressures of world crisis after world crisis keep them too busy to see each the way they want to and so they both resign themselves to sadness. Bucky’s having a hard time connecting to everyone on the Old Avengers team besides Steve, who has so many people caring for him these days that Bucky doesn’t really know what to do with himself. And one day he comes across the two most elusive Avengers, the two busiest ones who are never around, slow dancing to some classical waltz. Tony’s arms are wrapped around Thor, gently lowering his head into Tony’s neck in a surprisingly protective gesture, and one of Thor’s hands is over Tony’s heart. As Bucky watches, Tony’s heart begins to glow, his skin showering sparks as Tony laughs softly. “I’ll be up all night if you keep that up, Thunder Struck.”Tony says, turning electric blue eyes on Thor’s hand. Said hand drifts up to cup Tony’s jaw, turning it away from Bucky as Thor steals a kiss. “Sleep is just another death, Anthony, and I don’t want tonight to die. I miss you as soon as the sun rises - let me have a little longer.” Thor tells him and oh, oh shit, wow Bucky never realized they were together. He also never realized how beautiful they were together. Or how…lonely. When Tony leaves the next day, Bucky finds himself naturally drifting into Thor’s space and requesting his help with various tasks for the day. Then he finds himself checking that Thor is eating enough. And then he finds himself asking for book recommendations. When Thor leaves, a quizzical sort of smile on his face, Tony comes back and Bucky does the same thing. Tony is tiny and difficult to care for. It makes him feel…more like himself, really. Tony is easy to talk to. He wants to make Tony smile like Thor does.He keeps switching off between the two of them, carrying messages back and forth, and finally starts quietly threatening everyone keeping them as busy as they are. He chases off the other Avengers when they try to infringe on Tony and Thor’s private time. Then, to his utter bewilderment, he’s included in that private time. Then Thor’s hand, his other hand clutched in Tony’s to ground it, presses into Bucky’s. Tony is pressing a kiss to his neck with the slightest hint of teeth, making him shudder, and Thor brushes their entwined hands against Tony’s chest, sparking that beautiful glow Bucky has obsessed over for months. “He wants you, Soldier.”Thor says cheekily, glancing between Bucky and Tony under his thick lashes. Bucky is just…wow…he’s dying a little bit? Because he felt terrible about wanting Tony when he was such good friends with Thor, but Thor was looking very interested in what Tony was doing, and what Tony was doing was sucking a love bite into Bucky’s neck. Bucky squeaks out an, “Oh God yes.”Before finding himself in an incredibly hot threesome.