Okay, so, short questions with very long answers. I will do my best to keep things simplified but simplifying Bleach is difficult...
Bleach is a manga by Tite Kubo, with an anime adaptation (which is full of fillers, and stuff, and yeah... manga is better!) It was a long running one, from 2001-2016, and ended at 698 chapters, so it’s a pretty big time investment at this point (the anime, I believe, got cancelled and therefore isn’t complete).
Very basic overview of the plot is that there’s a teenage boy called Ichigo who can see ghosts and gets attacked by an evil ghost (known as a Hollow). He’s saved by a Shinigami (’soul reaper’ in English) and through various shenanigans ends up a Shinigami himself, and has to fight Hollows to protect the humans, etc. etc. etc.
There’s a “Soul Society” (alternate plane where the Shinigami live) which is the focus of the first couple of arcs, but then we meet “Hueco Mundo”, which is the plane where the Hollows live. This is the setting for what is, in my opinion, by far the best part of the series - the Arrancar Arc, where Ichigo&crew have to fight a bunch of super-powered Hollows (Arrancar) to save the world.
As this ask is mostly about Opaal, I’m gonna leave the basic plot explanation there, because Hueco Mundo is where Opaal lives.
I am, however, going to have to mention Hollows and Arrancar in a little more depth for him to make much sense. So.
Hollows are basically the souls of dead people who did bad things in their lives (mainly murder and the like). For the most part they don’t have memories of their human lives, but for all intents and purposes they’re a bunch of evil spirits that want to kill and eat you. They’re called “Hollows” because they have a hole somewhere (usually their chest) which represents the fact that they’ve lost their heart. Hollows also have “Masks”, which is a bone-like, well, mask, that covers their face and represents them not knowing who they are, etc.
Really quick, but there are four evolution levels of Hollow, from least to most powerful: Hollow, Gilligan, Adjuchas and Vasto Lorde. Hollows evolve by eating each other (basic Hollows only eat humans and that’s not enough for them to evolve, but if they start cannibalising each other then they get stronger). Most Gilligan lose their sense of self at that point and go back to terrorising humans, but occasionally they retain it and continue eating each other until they evolve to Adjuchas. Adjuchas is a terrifying state to be because they have to keep eating each other in the hopes they’ll reach Vasto Lorde, otherwise they de-evolve and lose their sense of self. Vasto Lordes are rare and ridiculously powerful.
Then we have Arrancar. Some evil mastermind decided to create an army of Hollows with reason, so very long complicated explanation skipped, he broke off their masks and voila, we have Arrancar, more powerful than Hollows and also mimic-Shinigami, in that they have a physical weapon that can power up, although in an Arrancar’s case, it causes them to physically transform into something stronger (think Bruce Banner and the Hulk, except the Hulk keeps Bruce’s mind). These guys are the best characters in the series (I love them so much), the strongest ten are ranked 1-10 and called “Espada”, and yeah. Best characters. You ever see me going on about Ulquiorra or Grimmjow, they’re Espada.
But I’m getting a little off-track... It was revealed at some point that while the evil mastermind decided to make an army by removing their masks, there are some Hollows who came to that conclusion all by themselves and tore their own masks off. These Arrancar, known as ‘self-made’ Arrancar, don’t owe their existence to evil mastermind and therefore don’t always serve him.
Hence, Opaal. This are his ref sheets I drew a couple of years back:
Opaal is a self-made Arrancar who is decidedly not loyal to evil mastermind and actively hates him (like most Hollows do, even the loyal Arrancar, he just happens to be stronger than them and in Hueco Mundo strength is everything).
He was an Adjuchas-level Hollow before he tore his mask off, so one of the ‘fight to evolve not de-evolve’ ones, which makes him reasonably powerful, but compared to the evil mastermind’s Arrancar he’s still weaker and probably couldn’t beat any of them in a fight. So he just hangs around in Hueco Mundo, fighting and eating Hollows in the eternal desire to be stronger.
He likes goading people, is generally annoying as hell, and has zero qualms about picking on anyone weaker than he is. On the other hand, he has very highly tuned survival instincts (doesn’t want to be anyone’s lunch himself!) and is normally good at avoiding anyone stronger than he is. That being said, if he does end up trapped with a stronger Hollow, he’ll fight tooth and nail to not die, and so far is managing to survive pretty well. There’s another self-made Arrancar he hangs out with sometimes, called Schinn @thetwelvecaesars‘ OC, although really it’s Schinn hanging with him for protection and Opaal deciding he’s not worth eating yet. Arrancar friendship is so caring...
He’s also stubborn and doesn’t accept help from anyone, although considering ‘accepting help’ basically equates ‘asking to be eaten’ in Hueco Mundo, that’s not a particularly unusual trait for a Hollow/Arrancar. One of his abilities is to drink water/douse himself in water (when he can - Hueco Mundo is a desert) to revitalise himself and give him the energy to get away, but on the down side as long as he’s using that power his healing is stalled, so it’s a quick escape but then he needs to hunker down somewhere safe to heal, otherwise he’ll end up collapsing because that only works for so long before blood loss becomes a problem.
So that’s a... brief introduction for you. Hope it explained things rather than made them more confusing...