Bisharp's Pokedex entries are a stream of awesomeness in line with its epic design, but honestly this Pokemon's dex entries just really make this mon pretty darn cool from an in-universe perspective. Some of the best ones though:
Black: It leads a group of Pawniard. It battles to become the boss, but it will be driven from the group if it loses.
Almost all of Bisharp's dex entries talk about how it leads an entire pack of Pawniard and hunts enemies together with them, but it's pretty interesting that Bisharp can very easily lose its position as leader if it loses. I imagine it would especially be the case if it meets another Bisharp who doesn't have a Pawniard pack to lead, where it will challenge a leader Bisharp and try to win: if the current leader loses, the Pawniard will no longer accept it as leader and drive it away, and then the winning Bisharp will be accepted as their new leader. The losing Bisharp is then on its own and has to find another Bisharp it can beat and try to steal another Pawniard pack, and so on. It's a never ending cycle and it seems to imply that Bisharp are constantly competing to lead packs of Pawniard, especially if one is driven from a group because it lost and now has to find a new Pawniard squad to lead.
It's even more interesting when you take into account Pawniard's Shield dex entry:
"A pack of these Pokemon forms to serve a Bisharp boss. Each Pawniard trains diligently, dreaming of one day taking the lead."
Most Pawniard are totally subservient to their Bisharp boss, and would not even think of betraying it, but at the same time each one is preparing for the day they eventually become a Bisharp and become a leader themselves. I would assume one scenario is that one would evolve in the event that they lose their Bisharp leader and are left leaderless, making one Pawniard become a Bisharp and take the lead. But if one were to evolve even when the pack still has a leader, then it would create a rivalry. The newly evolved Bisharp would have to battle the current leader Bisharp, which threatens the current Bisharp leader's position and thereby would lead to either the newly evolved one taking over, or it being driven away and needing to find its own pack of Pawniard to lead.
Speaking of which, the former scenario can possibly happen in one particular circumstance, as per Bisharp's Ultra Sun Dex entry:
Ultra Sun: No matter how strong the Bisharp, it's said that if the blade on its head is chipped, it will retire from its position as the boss.
Yeah. While Bisharp are almost always leaders of a pack, the blade on their head is a distinct pride and honor, and if that breaks, a Bisharp will step down from its position eternally and revoke its own right to ever lead a pack again, becoming a lone hunter for the rest of its life. Definitely adds an interesting layer to its behavior. In such a case, that means the pack of Pawniard is left without a leader, and since each one trained diligently in hopes of becoming a great Bisharp one day, that means one of them will have to evolve and become the pack's new leader.
In general the other dex entries are pretty awesome:
BW2: This pitiless Pokemon commands a group of Pawniard to hound its prey into immobility. It then moves in to finish the prey off.
Ultra Moon: It leads a group of Pawniard. Bisharp doesn’t even change its expression when it deals the finishing blow to an opponent.
Sword: It's accompanied by a large retinue of Pawniard. Bisharp keeps a keen eye on its minions, ensuring none of them even think of double-crossing it.
Shield: Violent conflicts erupt between Bisharp and Fraxure over places where sharpening stones can be found.
You can get a general grasp of Bisharp's cruel and merciless personality in the first three listed here. It has no sense of pity or empathy for its targets and will not hesitate to kill them without any sense of emotion to it. Very befitting of a Dark-type hunter. Its mob boss vibe is also enforced not only by having Pawniard do the bulk of its dirty work but also in that it's very observant of its cronies to ensure its authority is never challenged.
The Shield dex entry is fun because it's yet another Pokemon-Pokemon interaction: Fraxure have the sharpen their tusks but Bisharp and Pawniard have blades to sharpen as well and they are constantly rivaling for spots to sharpen their blades with Fraxure. A pretty interesting relationship. I suppose Haxorus need not sharpen its tusks though, or maybe Bisharp don't even think of crossing blades with that.
Such a great Pokemon but it's truly a fitting Pokemon for the Dark-type as a merciless hunter and mob boss with quite a bit of depth to its in-world behavior.