Ichigo Kurosaki may be the hero of Tite Kubo's manga/anime series Bleach, but his father, Isshin Kurosaki, may set the best example of all. Though for a long time, his secret significance was kept secret from fans.
Isshin is introduced simply as Ichigo's wacky father and, at first, he seemed completely oblivious to Ichigo and Rukia's Soul Reaper ways. But this was all a facade. Ichigo's father was a Soul Reaper before Ichigo was ever born, and he knows the ways of zanpakuto and hollows as well as any Captain. Secretly, he rebuilt his old Soul Reaper powers bit by bit until he was ready to take on hollows once again, and even teach Ichigo a thing or two about fighting. And all the while, he continued to run the Kurosaki clinic and be an outstanding parent to Ichigo, Yuzu and Karin. His life's story is a humble but remarkable one.
Ichigo's Father Is A Hands-On Captain
Partway through the Thousand-Year Blood War arc, the reader fully dives into Isshin's backstory for the first time. Around 20 years ago, when Masaki and Ryuken Ishida were high school students, Isshin Shiba (of the esteemed Shiba clan) was the Captain of Squad 10. As a powerful Captain and a nobleman, he had it all, and he and his Lieutenant Rangiku Matsumoto enjoyed dumping all their paperwork on poor Toshiro Hitsugaya. These carefree times would end, though, when an alert came up: a powerful and strange hollow was rampaging around in the world of the living. Isshin didn't like paperwork much, but he was always up for a fight, and he soon confronted the hollow.
But this was no ordinary hollow. It was White, a special hollow that Sosuke Aizen had crafted, and this hollow soon endangered Masaki's life. The few remaining Quincy on earth (including Masaki) did what they could, but only the power of a Captain like Isshin could handle White. Isshin's shikai was enough to subdue this hollow, and Aizen scrapped his creation as a failure. Isshin was unaware of Aizen's involvement, but he did make a bold decision to save Masaki's life. She lay dying, but with Kisuke Urahara's help, Isshin lent her his Soul Reaper powers and he converted into an ordinary human as a result. Isshin knew that would happen, and he had no qualms about it, surprising even Kisuke. If he can't even save one teenage girl's life, what kind of Captain is he, after all?
Isshin Kurosaki Is the Ideal Family Man
Once he became Isshin Kurosaki, Masaki first became his friend and then, his wife. Not much is seen of their dating life, but Isshin says that whenever he smoked, his wife would call him "cool," and this is why cigarettes have a special place in his heart. As two ordinary mortals, they had a son, Ichigo, upon whom Masaki doted, then twins, Yuzu and Karin. Then Grand Fisher came along.
As seen early in Bleach, Grand Fisher lured Masaki away and killed her right in front of young Ichigo's eyes. Now Isshin was a single parent, and he assumed this responsibility with grace. He doted on his two daughters and was a bit tougher on Ichigo, but he certainly loved the boy. Isshin the goofy Captain was now Isshin the goofy father, and by the events of Bleach, Yuzu really looked up to him while Ichigo and Karin scoffed at his nonstop antics. All this was just hiding Isshin's pain, though, including his fall from Captaincy and then the death of his wife. He makes sure to visit her grave regularly (though he goofs off even then).
It was a shock when Isshin donned the robes of a Soul Reaper once again. Ichigo was away and Kon was running around in Ichigo's body, and Grand Fisher (now a primitive Arrancar) was rampaging once again. Isshin confronted the beast, lectured him on the nature of zanpakuto, and slew him. Not long after this, Kisuke came by to chat, and they agreed that the Arrancars were a grave threat. Not long after that, Isshin visited Ryuken Ishida, and they commented on how their respective sons were ready to make their own decisions.
Most Importantly, Ichigo's Dad Is A Selfless Figure
All of Isshin's actions so far, and the ones to follow, reinforce the concept that he is a selfless and uplifting figure. Isshin had no interest in taking down Aizen alone; he's not here to hog the spotlight. Instead, he helped Ichigo unlock the true potential of Zangetsu, and father and son faced the traitor Captain together. Then, with Kisuke's help, Aizen was taken down for good, and Isshin was perfectly happy to return to his deceptively ordinary family life at the Kurosaki clinic. As far as he was concerned, he'd worn the robes of a Soul Reaper for the last time.
Isshin put duty first, and personal glory a distant second. In fact, even as a Captain, Isshin complimented Toshiro on his excellent work ethic, rather than playing up his own strengths. Isshin gave up this entire life to save Masaki, and it never even occurred to him to let her die or try to save her and keep his powers. Duty came first, and he'll pay any price for that. Then, he became a responsible and protective single parent, and he was there when Ichigo needed help against Aizen. Isshin Kurosaki is the humble, selfless sort of hero, which allowed Ichigo to be born and later, to triumph over Sosuke Aizen for all time.