Some Gundams I would say, especially Iron Blooded Orphans. The story of Orga and Mika was really tragic. This is gonna contain spoilers so beware.
I think it captures the essence of a relationship between two friends which seems like a neverending bond of trust but in actuality is a toxic and unhealthy one which eventually leads to the death of both and a disaster. If we start with Mika, he got saved by Orga as a child and decided to follow Orga anywhere. No matter what Orga decides, Mika backs him up. As an orphan who knows nothing but how to fight and kill, he kills whoever Orga points at.
But this also effects Orga, since Orga is pushed by the pressure to doing some stupid decisions because of Mika, since Orga needs to show how tough, competent and fearless he is to Mika. Best example is in the final third of the show, the Iron Blooded Orphans has gotten out of most trouble and isn’t the public enemy number one anymore after some political shenanigans and cleaning their names for the whole season basically, and they should’ve and could’ve just quit at that point.
But Orga feels like the show must go on and they can’t satisfy and should reach for bigger things with the pressure from Mika as he wants to be a good and fearless role model, and with Mika not being able to say no to Orga and only knows how to fight for him, they hype each other up for dumb decisions, leading to the Iron Blooded Orphans coming back for more, causing more political mess and death, leading to the end where Orga, Mika and like 90% of their crew die, only because Orga and Mika decided to push each other further and not satisfy in staying away from the battlefield.
I find this a very interesting story and as someone who loves tragic stories with not all happy happy endings, I’d rank IBO’s plot as one of my favorites. It’s like Simon and Kamina from TTGL but gone wrong.