During Bleach, many unforgettable characters grace the screen during battle, and the first is Rukia Kuchiki, a Soul Reaper (and she's the one who gave Ichigo his powers). But Rukia isn't the only Kuchiki around here; there is also her Captain and foster brother, Byakuya Kuchiki.
Captain Byakuya Kuchiki is in charge of squad 6 of the Soul Reapers' forces, and he is also the head of the noble Kuchiki family. This means that he has a lot of responsibilities, and he plays a major role in Rukia's life and through her, Ichigo's. He is capable of many things, but sometimes, Byakuya falls short in minor (or serious ways).
10 Strength: Expert Flash Step Technique
Although Byakuya Kuchiki isn't quite at the top when it comes to the flash step (more on that soon), he is still more proficient at this technique than most other Soul Reapers are. Long has Byakuya practiced the flash step until it became second nature to him.
The flash step allows a Soul Reaper to rapidly move from one point to another in a straight line, and it allows Byakuya to avoid enemy attacks or approach the enemy. He can outpace Rukia or even his own Lieutenant, Renji Abarai.
9 Weakness: Overconfident
If Byakuya isn't the #1 user of the flash step technique, then who is? That would be Yoruichi Shihoin, who has known Byakuya since his boyhood. She is known as the "goddess of flash," and for a good reason. She can outpace Byakuya if she puts her mind to it.
Byakuya tried to keep up, and he vainly presumed that he could outpace Yoruichi as of the Soul Society arc. But he was proven wrong when he faced Yoruichi directly, and he ended up looking like a fool.
8 Strength: Noble Influence
Not much of this part of Byakuya's life is seen, but he is the head of the Kuchiki family, which in turn is one of the four great noble families of the Soul Society (alongside the Shihoin family). In a world like this, it pays to be a nobleman or noblewoman.
Byakuya no doubt has a lot of social influence owing to his position, coming with all kinds of lofty privileges that Ginrei Kuchiki handed to his grandson. Few events take place in the Soul Society without Byakuya being involved or at least knowing about it.
7 Weakness: Potential For Hostages
On the other hand, having such a wealthy and prominent family comes with its fair share of risks. A significant risk that the rich and powerful face is the potential for their enemies to take family members hostage and threaten them to gain leverage. In Bleach, the wealthy Marechiyo Omaeda had his family threatened by Sternritter K, BG9. It stands to reason that Byakuya might one day have a similar situation play out for him, and he wouldn't like it.
6 Strength: Kido Arsenal
Soul Reapers have more than their zanpakuto for fighting their enemies. Most Soul Reapers are also able to perform kido spells, which can trap an enemy, block an attack, or (most often) deal damage somehow. There are many spells to choose from.
Byakuya made sure that he didn't fall behind in this department. He's not the #1 kido expert, but he's still able to cast powerful spells elegantly during combat, such as Riku Jokoro (his favorite) or Byakurai (a narrow but powerful offensive spell).
5 Weakness: Complacency
Byakuya is a quietly proud Soul Reaper who is very comfortable with his powers & position, and anyone with his prestige would feel pretty good about it. But once in a while, he gets a little too used to his comfortable place in the world.
He arrogantly presumed that he had outmatched Yoruichi in the flash step, and he was proven wrong. By the time Sternritter As Nodt stole Senbonzakura, Byakuya's bankai, Byakuya had grown complacent with that, too. Not good.
4 Strength: Powerful Zanpakuto
Here is another category where Captain Kuchiki may no be #1, but he is still among the elite and has every reason to be proud. His zanpakuto, as mentioned earlier, is Senbonzakura. Its shikai can form a thousand blade fragments that look like pink blossom petals.
This shikai is powerful enough to subdue most of Byakuya's enemies, and in the rare case where that's insufficient, he can use his mighty bankai, Senbonzakura Kageyoshi, which has a few tricks of its own. No one survives facing this bankai, not even the 7th Espada, Zommari Rureaux.
3 Weakness: Inflexible
Byakuya was law-abiding to a fault and this caused some serious strain between him, Rukia & Ichigo. The scheming Captain Sosuke Aizen wanted Rukia dead and that meant sentencing her to an unfair execution.
Byakuya was so fixated on following the law, he upheld Rukia's cruel fate and defended it, unwittingly playing right into Sosuke Aizen's hands. This is the main reason why Ichigo and Byakuya were feuding during the Soul Society arc.
2 Strength: Newfound Humility
This ties into a few of the earlier entries about Byakuya Kuchiki. He was arrogant about his abilities and his role in the world, and really starting to pay the price. But once he tied against Ichigo in battle, and lost to As Nodt, he began to change that.
Now he is confident but humble, and Byakuya knows that he has his limits like anyone else. He has become kind to Rukia and Ichigo, seeing them as friends and allies rather than subordinates. He also learned to not take Senbonzakura for granted.
1 Weakness: Unresolved Grief
For a time at least, Byakuya was haunted by the loss of his wife, Hisana. Unusually, Byakuya married outside of his class, since Hisana was a poor woman from the Rukongai district, rather than a noblewoman. She died of illness only a few years into her marriage to Byakuya.
Hisana death, and Byakuya's frowned-upon marriage, had a negative impact on him. He processed his grief by becoming fanatical about the law and having a distant relationship with Hisana's little sister, Rukia. He needed a better way to cope with all this, and he could have turned out a little better.