While I'm still shouting into the void about umbrella academy, we do NOT nor have we EVER talked enough about Five's relationship with Reginald. Baby the NUANCE!! And we could have had even more, but I'll focus on what we did get.
No one ever talks about Five being Reginald's clear favorite. No one talks about how Five, completely contingent on his experience getting trapped in the apocalypse, respects and understands Reginald better than any of the others.
Reginald is an evil, selfish mother fucker, but he's pretty consistent on one aspect: he values intelligence and restraint above all else. For one example, we see the kids running drills/racing up the stairs in a flashback and Five starts teleporting. Diego immediately calls this cheating, to which Reginald responds that Five did the right thing and "adapted" to win- he used his smarts to beat the game, and winning is far more important than meaningless honor to him. When Five argues with Reginald about time travel, Reginald calmly rebukes him on the basis of sense, and when Five runs out on his own, Reginald does nothing.
But not because he doesn't care, like he clearly feels about the other children. No, because he puts a damn giant portrait of Five up on the mantlepiece and keeps track of every day he's gone after that. Clearly he hopes Five will return. There's no reference to Ben or concern for him apart from a statue outside that seems to be there more to punish his siblings than anything else. The reason he doesn't go after Five is simply because he knows he can't convince him, so the boy will either be smart enough to survive somehow or he will die. He recognizes Five's intellect once again in season 2, when the team gathers for the disastrous dinner in 1963 Dallas. He gets annoyed with the rest, belittles them, and dismisses them altogether, bothering only to address Five after that.
So what about Five? The only time we see him directly interact with Reginald as a kid is their argument, but as an adult, when he returns? He makes a number of comments about how Reginald was right, and in 1963 his hail mary is going to him for help- because clearly based on his actions, Reginald is the only person on Earth Five thinks might be smarter, or wiser, or simply more informed on certain issues than himself. He is quite literally the only person Five truly respects. But yet he doesn't even like him. He knows what an asshole Reginald is and often refers to him as such, he sees and acknowledges how much that man's actions fucked up his siblings. In fact at one point he even states that (despite his apocalypse trauma) if he had stayed in that house until adulthood, he would have been every bit as messed up and broken as all of his siblings. So why does he still defer to him? Why does he behave even when Reginald goes out of his way to demean his siblings in front of him, doing his best to maintain the man's respect?
The only reason can be his time travel. He escaped the abuse early, and his worst trauma was a result of not listening to Reginald. So despite everything, hello Mr. Nuance, Five still desires Reginald's approval and looks up to him... Like a child, even. Despite his age... Just like his siblings.
Reginald and Five also understand each other and have the most similar ethos. They both believe in doing whatever it takes to achieve one's goals, morals be damned. I believe this is something else they see in each other that allows them to get along better than the rest.
But Five also loves his siblings. That's not something Reginald can claim. In fact, he'd see it as a sentimental failing. Five seems to almost resent himself at times for it too, but unlike Reginald, Five is sentimental. About his siblings at least. Because from the moment they get separated he realizes with startling clarity that they are the only thing that matters to him, his one goal that he is going to chase no matter who he has to kill or fuck over. I truly believe that Five didn't just come back because he'd been trying and wanted to escape the apocalypse and then the commission. He did it because he couldn't stand the idea that his siblings lived horrible lives, grew up to be miserable, and then died young and unhappy and scattered. He came back to stop the apocalypse and went against everything up to and including the universe to give his family a chance to be happy.
So there you have it. Five and Reginald's "I could write an academic thesis on the intricacies" relationship.
