Anime often portrays female characters as tsundere (outwardly aloof but secretly has a soft side), but several of the male characters in Bleach show clear tsundere traits. The protagonist Ichigo Kurosaki might be the most prominent example, but he's not even the best example of the archetype in Bleach. That honor goes to Kenpachi Zaraki, who hides his warm heart behind gruff exterior and brutal ways as a Soul Reaper Captain.
Kenpachi Zaraki, The Scary Coach
Kenpachi Zaraki did not have a happy childhood. As a boy, he roamed aimlessly in the poorest region of the Rukongai district. But He faced great struggles but survived. Eventually, he obtained a fallen Soul Reaper's zanpakuto and became a wandering swordsman. During this time, he faced another swordsman ruffian named Ikkaku Madarame and defeated him. For honor's sake, Ikkaku wanted Kenpachi to finish him off, but Kenpachi refused. The reason he gave Ikkaku was that dying on purpose was idiotic. For the sake of strength and glory, Ikkaku should survive and train hard to become stronger, so he may be the victor next time.
This made a big impression on Ikkaku, who became the third seat of Kenpachi's squad years later. It's likely that Kenpachi said that so no one else would have to suffer despair and die a pointless death. Perhaps Kenpachi was burdened with despair at the time, and he was desperate to rescue other people, like Ikkaku, from similar feelings. He stoked a fire in Ikkaku's heart, and it turned Ikkaku's life around.
As a Soul Reaper Captain, Kenpachi is all about strength and attitude, and he claims that his squad (#11) is all about "live or die on your own merits." But despite that unspoken rule, Kenpachi went to great lengths to train his men, and later during the Thousand-Year Blood War arc, he took it upon himself to face the mighty Sternritter so his men wouldn't have to. Kenpachi was always eager to train his subordinates, and in his own gruff way, he cared greatly for them, probably seeing them as younger brothers who needed guidance. But that's not Kenpachi's biggest tsundere trait. There's also the matter of Yachiru Kusajishi.
Kenpachi, Soul Society's Best Dad
During his days as a wanderer, Kenpachi met a young girl named Yachiru, who was not at all afraid of Kenpachi's menacing aura or sword. Yachiru insisted on keeping Kenpachi's company, and so, Kenpachi was inspired to unofficially adopt her, and he roamed the world with Yachiru clinging to his back or sitting on his shoulders. Later, Yachiru became the Lieutenant of Squad 11. Kenpachi looked after her as not just her friend, but as a boss. Kenpachi wouldn't go anywhere without her, and when he ran around the huge Soul Society to hunt down Ichigo, Yachiru came along and tried to guide Kenpachi to his target (her directions were faulty).
It was played off as comic relief, seeing a funny little girl giving bad directions to her huge and scary Captain, but it really deepened and broadened Kenpachi's character. He looked more like a doting father than a boss, and that trend continued into the next few story arcs.
When Kenpachi arrived in the desert world of Hueco Mundo, he gruffly but earnestly helped Ichigo take on Nnoitora Gilga, saying "you've done enough. Let me take over," rather than let Ichigo die. At some point, Kenpachi was wounded and knocked down, and Nnoitora tried to attack Yachiru next. Horrified, Kenpachi leaped to his feet, assumed an overwhelming (and skull-shaped) aura, and delivered a mighty blow that kept Yachiru safe.
Amusingly, when Yachiru warned Nnoitora about Kenpachi being protective of her, Kenpachi simply denied it, playing into the tsundere trope even more. Kenpachi proceeded to defeat his Arrancar foe after a difficult clash.
Kenpachi was nearly in hysterics when Yachiru went missing during the final battle against the Sternritter, and he barked at his men to find her at all costs, regardless of the danger to their lives or Kenpachi's. By the series' end, Kenpachi is still Squad 11's Captain, and Yachiru is still by his side as a loyal friend and unofficial foster daughter. It's true that some other Bleach characters have some vague tsundere traits, such as the uptight Uryu becoming Ichigo's friend while refusing to admit it.
But seeing such warm, fuzzy tsundere feelings in a scary package like Kenpachi Zaraki is far more impactful, and the contrast is both amusing and delightful. No one could sweetly adopt a little girl and then deny their feelings quite like Kenpachi Zaraki.