Rukia Kuchiki is the current captain of the 13th division of the Gotei 13, having replaced her former captain Joshiro Ukitake after his death. Rukia plays a prominent role in kicking the story off and, after regaining her powers, she's a useful combatant.
Her humble attitude and determination makes her a likable character. Throughout the series, she continues to grow and by the end of it, she's able to go into Bankai mode. In this state, Rukia becomes encased in ice and she gains the ability to freeze her opponents to the temperature of absolute zero. Just coming into contact with her is enough for her enemies to be frozen stone cold. With such a power, Rukia can easily defeat some of Bleach's strongest warriors but would struggle against others. These are 5 characters Rukia can beat in a fight and 5 more she'd have trouble with.
10 CAN BEAT: AS NODT
A member of the Quincy's Sternritter unit, As Nodt, is a religious man who strongly believes in the concept of heaven and hell. He spent much of his life sick and in pain, so what As Nodt feared most was going to hell, believing that if he was sent to hell, his suffering would only increase. As he was about to die, the leader of the Quincy, Yhwach, offered him power.
As Nodt took that power and became known as "The Fear", and with this power, he became one of the strongest Quincy. Despite his strength, he was no match for Rukia and her Bankai, as he was instantaneously frozen to the core after approaching Rukia.
9 CAN'T BEAT: TOSHIRO HITSUGAYA
Toshiro is the captain of the 10th Division of the Gotei 13. Both him and Rukia are regarded as young Soul Reapers, despite being a few hundred years old. They both also shun during their time at the Shin'o Academy. Both combatants are also users of ice-based Zanpakutos, with Toshiro's sword being the more mature at this point.
Rukia would put up a strong fight against Hitsugaya and her absolute zero ability would give her a good chance. But, at the end of the day, Hitsugaya is more adept at using his abilities and his Bankai maturing towards the end of the series puts it in a different bracket.
8 CAN BEAT: ISANE KOTETSU
Isane Kotetsu is the current captain of the 4th division in the Gotei 13, replacing Retsu Unohana after her death. Isane is a rather meek and timid girl in her daily life, seeking to go under the radar as much as possible. Despite this, she is brave enough to stand and fight against opponents she knows she has no chance against.
This bravery would serve her well in a fight against Rukia but, ultimately, it might be her downfall as well. As a captain, Isane's strength can't be laughed at but, when it comes to a straight-up fight, Rukia would win.
7 CAN'T BEAT: RETSU UNOHANA
Retsu Unohana, formerly known as Yachiru Unohana, is a legend amongst legends in the Gotei 13. Upon the founding of the Gotei 13 by Genryusai Yamamoto, Unohana was chosen to be the first Kenpachi. The title Kenpachi usually goes to the most bloodthirsty and physically powerful fighter in the Gotei 13.
For a long time, she served that role until she decided to take over the 4th division as a healer. But even then, her skills hadn't waned, and she fought on footing with none other than the nigh immovable Kenpachi Zaraki. Unohana is one of the strongest women in Soul Society's history, meaning that, for now, she is out of Rukia's league.
6 CAN BEAT: RANGIKU MATSUMOTO
The Lieutenant of the 10th division of the Gotei 13, having previously graduated from Shin'o Academy. Rangiku has come a far way since her days of being a poor and starving child. Now a mature and experienced fighter after years and years of fighting, she can hold her own in the toughest situation.
Her Zanpakuto, Haineko, turns her blade to ashlike razor blades that she can control at her will. Rangiku can cut anywhere she has ashes but this wouldn't get her far against an ice-encased Rukia. Rangiku's 'not so fast' speed also means she would struggle to avoid Rukia's absolute zero ice attacks.
5 CAN'T BEAT: TIER HARRIBEL
Tier is the current leader of Hueco Mundo, having taken over from Aizen after his defeat and subsequent imprisonment. Harribel is a quiet and peace-loving person who prefers not to spill blood. But, if it comes down to a fight, she is confident in her abilities to defeat whatever foe stands before her.
Her water-based abilities could massively hinder her in a battle, as it did when she went up against Toshiro Hitsugaya. But her superior strength as a fighter should see her claim victory over Rukia, if only just.
4 CAN BEAT: AARONIERO ARRURUENE
Aaroniero Arrurune was an Arrancar that fought against Rukia in Hueco Mundo. He believes himself to be a being that is constantly evolving, through devouring thousands of souls. With every soul, he becomes stronger, but also a bit more unhinged and insane. He has a split personality that manifests as two different head, and can oftentimes be seen reacting in a contradictory manner.
Rukia defeated it back in Hueco Mundo and, since then, she's developed a Bankai, meaning that she would have an easier time slaying the monster were they to do battle again.
3 CAN'T BEAT: BYAKUYA KUCHIKI
Byakuya adopted a young Rukia Kuichi after having encountered her at the Shin'o Academy. Byakuya did this upon the request of his dead wife, who wanted Byakuya to find the sister she had abandoned while still a child.
Rukia's newly developed weapons and ideas mean she stands a far greater chance now than she has ever done in her entire life. But Byakuya's mastery of his own Bankai means its a hundred years too soon for her to best her brother.
2 CAN BEAT: ORIHIME INOUE
Orihime is a graduate of Karakura High School and the mother of Kazui Kurosaki. She's a kind and sensitive soul and, after being attacked by a hollow, she becomes spiritually aware and manifests powers later on.
Her Shun-Shun Rikka techniques helped her to defend against a lot of the lower-level threats in Bleach, but Rukia would be a massive step up. This massive power gap means that Orihime would lose if she had to fight Rukia one on one. Rukia has far more fighting experience, as well as a fighting style suited for battle.
1 CAN'T BEAT: YORUICHI SHIHOIN
Yoruichi was once the captain of the 2nd Division in the Gotei 13, as well as commander of the Stealth Force. Having been born a princess in a noble household, great things were always expected from Yoruichi and she delivered tenfold, before relinquishing those titles.
Yoruichi is one of one the quickest characters we see in the series, meaning she would be able to land hits on Rukia, who is considerably slower. Yuroichi's Thunder Beast form has enough speed and thunder to defeat Rukia, even with her incredible Bankai.