Bleach revolves around the black-robed Soul Reapers and their mission to slay monstrous Hollows and guide the souls of the dead to the afterlife, or the Soul Society. Soul Reapers are all capable fighters wielding soul-cutting swords known as zanpakuto, but some are far more powerful than others.
Captains and Lieutenants are the highest-ranking officers, and for millennia, the ancient and powerful Captain-General Genryusai Shigekuni Yamamoto commanded the Soul Reapers as the wisest and strongest of them all. He left some big shoes to fill when he died in the "Thousand-Year Blood War" arc, and someone else had to lead the Soul Reapers into a better future.
Who Will Replace Yamamoto as Bleach's New Captain?
Captain Kyoraku Shunsui was the Soul Society's strongest surviving Soul Reaper after Yamamoto's death, and for many reasons, only he was fit to become the new Captain-General of Squad 1. Captain Ukitake was almost as experienced and powerful, but he was ill and had to settle for commanding Squad 13. Meanwhile, Captain Unohana Retsu was preoccupied with other matters and was unable to assume command.
Kyoraku Shunsui possessed the right personality, influence, and experience to succeed Yamamoto as head Captain, as well as the mental fortitude to match his combat prowess. He was born into the noble and distinguished Kyoraku family, which gave him a significant advantage. Shunsui was also personally connected to the powerful Ise family through his deceased brother, which explains why Lieutenant Ise Nanao is so loyal to him despite their clashing personalities.
Most significantly, Shunsui was a Soul Reaper officer with centuries of experience by the time the "Soul Society" arc began, and he and Ukitake were among the first Shin'o Academy alums to be promoted to Captain. Even in the 110-year-old Bleach flashback, Shunsui had already served for a considerable amount of time and was well-liked and respected by everyone in his vicinity. Even though he had a silly personality and a drinking habit, Shunsui took his duty very seriously. When his friend and mentor Yamamoto died at the hands of king Yhwach, Shunsui immediately knew what needed to be done.
He assumed command at once as the new Captain-General and transferred to Squad 1, to which no one objected. The surviving Captains were shaken by the Wandenreich's assault and needed a leader, and Shunsui quickly got them in line when they started squabbling among themselves. He had the heart of a true leader and soon led a counterassault on the Sternritter, eventually claiming victory over them with Ichigo's help. As of the new one-shot Bleach chapter, Shunsui remains Squad 1's commander and the Soul Society's strongest Captain.
In Bleach, How powerful is Shunsui?
Since Bleach is an action shonen series, the strongest Soul Reaper must also be the most effective fighter, not just the one with the most authority. As expected, Kyoraku Shunsui is enormously powerful, even if he rarely demonstrates his strength compared to the likes of Captain Zaraki Kenpachi or Captain Kuchiki.
Shunsui has a tremendous natural talent in terms of endurance, speed, swordplay, physical power, his use of kido spells, and more. He is a skilled veteran and a noble-born soul. His shikai, Katen Kyokotsu, gives him a variety of unexpected combat abilities, and he even simultaneously wields two zanpakuto. Similar to Squid Game, this shikai can turn kid-friendly games into extremely dangerous situations, and only a skillful and instinctive foe like Coyote Starrk has the slightest chance of surviving against it.
Finally, Shunsui's complex bankai, Katen Kyokotsu: Karamatsu Shinju, inflicts incredible damage on an opponent based on different phases of a grim story -- including drowning them or covering them in wounds -- and he can even challenge the elite Quincy, the Schutzstaffel, with this Bankai. Time and again during the final battle against Aizen's army or the Sternritter, Shunsui used his shikai and bankai alike to prove that after Yamamoto's unfortunate demise, he was truly the #1 Soul Reaper in Bleach -- and the only one fit to become the new head Captain.