My definition of "MCU" includes the tv shows (that I've seen). With this in mind, in no particular order:
1) Agatha Harkness & "Teen" ( spoilery identity is spoilery ) ,
Agatha All Along: I adored this show in 2024 when it was released and I still adore it, and have rewatched it three times already. There are many reasons why, but the relationship between these two characters is most definitely one of them. It has different layers, not least because the characters are both holding back information about each other and their true reason for the show's quest for a considerable time, and yet they bond in a very real way even before the various reveals. It ends up as mentor/protegรฉ, with a sideline of odd couple and sort of, kind of, family. And I really hope that whatever the MCU future brings, we will see these two together again.
2) Jessica Jones & Matt Murdoch,
(The Defenders): speaking of combinations I hope to see again - The big crossover miniseries of the Netflix Marvel shows was flawed in several ways, but the various combinations of characters were all gold, and I loved the Mattt & Jess combo most of all. To put it as unspoilery as possible: their different ways of reaching the top of a building had me in stitches. And the serious character scenes were fantastic. That neither of them was sexually interested in the other might have been why they got along so well, given both characters have a really messy love- and sex life.
3) Tony Stark & Bruce Banner, (
The Avengers): their scenes were such an unexpected delight. Very differnet personalities, and yet a meeting of the minds, so to speak, and great chemistry to boot. We hardly saw them in the same room again after
Age of Ultron, which I regretted, but given the ensembles grew larger and larger, it was probably inevitable. (Also, the writing for Bruce Banner changed a lot.)
4) Yelena Belova & Alexei Shostakov, (
Black Widow, Thunderbolts): I was torn between this and Yelena & Natasha, and Yelena & Kate Bishop, but Alexei wins with a combination of the relationship being showcased in two different movies and the way we see it change through said movies. Also: Alexei may have been a deadbeat (spy) dad, but he can make Yelena smile (intentionally, I mean, not just when he's being goofy) in an incredibly touching way. Again in both movies.
5) Nebula & Gamora (both of them),
Guardians of the Galaxy,
Avengers: Infinity Wars and
Avengers: Endgame: pace Yelena & Natasha, but these are my favourite sisters in the MCU. They get introduced as a seemingly straightforward rendition of bad girl and good bad girl, the evil and the heroic sister - and then it gets complicated. Given their incredibly screwed up childhood and youth (Thanos trying his best to win the worst Dad competition in the MCU), it's a miracle they had non-hostile feelings for each other to begin with, and yet they do. The moment in Guardians 2 when we find out what Thanos did each time Gamora beat Nebula in a match is absolutely gut wrenching. And when we see them connect and change through sevearl movies, it is both touching and absolutely cheerworthy.
6) Mark Spector & Steven Grant, Moon Knight: that they're both played by Oscar Isaacs is the least of it. The miniseries was so clever in the way it introduced us to them which turns certain tropes on their head because
( it gets spoilery )The result is a sort of "unknown and seemingly very different brothers find each other" tale which also manages to be self exploration and offers moments of grace, support and love in the last three episodes that still make me reach for my hankerchief upon rewatch.
Not included:
Peggy Carter & Dottie Underwood (
Agent Carter), because the subtext is barely sub, and I definitely ship them, which makes them disqualified for a list of platonic relationships (which I want to remain platonic). But they definitely had "my best enemy" potential in that show. And fantastic chemistry.
The other days