Tite Kubo's hit series, Bleach, is a classic shonen story. But in some regards, the audience is getting four for the price of one.
The series is content to radically change its setting, stakes and characters regularly to keep things fresh and provide a chance for the author to show off his creative chops. This isn't nearly done to the same extent as One Piece, where Luffy's crew explores countless islands and their unique inhabitants. Still, for a series that doesn't involve dozens of islands, Bleach does a fine job hopping from one idea to another while maintaining tight cohesion in the overall story.
Monster Hunting
The first leg of the story is the Agent of the Shinigami arc, which has some elements of a "monster hunter" anime like D.Gray-Man, Demon Slayer or Fire Force. Ichigo is thrust into the world of monsters and swords when the Soul Reaper Rukia Kuchiki pierces him with her zanpakuto to lend him her powers, which awakens Ichigo's own formidable latent abilities. Now, he is a Soul Reaper, too, and like a superhero, he has to keep this quest a secret while jugging a dual lifestyle. He's still a high school student, after all, and Rukia even transfers there as a student.
This continues for a handful of episodes until Rukia is called back to her home, the Soul Society. She's in trouble; lending Ichigo her powers was a grave offense, and she is escorted back by Byakuya Kuchiki and Renji Abarai. Ichigo is injured and left for dead, his hollow-hunting days now behind him. But he's not done yet; if he can't slay hollows, then he can rescue his new friend, and that will require an upgrade. It's time to switch gears to the isekai genre and invade the Soul Society.
A New World
Ichigo trains with Kisuke Urahara to restore and upgrade his abilities, and he now wields the zanpakuto known as Zangetsu. But he's not going alone: his friends Chad, Orihime and Uryu are with him, with Yoruichi the talking cat as an escort and guide. They are stunned by the sight. Soul Society is a vast, peaceful world modeled after pre-industrial Japan, and magic and swords are commonplace here. Storming the Gotei 13 to rescue Rukia means getting fired out of a magic cannon courtesy of Kukaku Shiba, and the quest is on.
Soul Reapers are the enemy, and they will risk their lives to uphold Rukia's execution and capture the "ryoka," or intruders. This arc has classic shonen action and drama throughout, and Ichigo is in for some surprises. He convinces Renji, Rukia's childhood friend, to support his cause, and Renji now trusts Ichigo completely. In addition, a strange power is emerging inside Ichigo, one that wields a hollow-like mask. With the help of Yoruichi (who is in fact a Soul disguised as a cat), Ichigo learns bankai at last, and challenges Captain Byakuya Kuchiki. It's a draw, and Byakuya is inspired to accept Ichigo's viewpoint and protect Rukia from the cruel laws of the Soul Society. But another threat arises: Captain Sosuke Aizen.
Aizen's Grand Plan
Sosuke Aizen is deeply ambitious and egomaniacal, despairing the lack of a god or leader in the heavens. He resolves to become that supreme being and steals the mystical Hogyoku from Rukia's body to unlock that power. He and Captains Ichimaru and Tosen flee to Hueco Mundo, and Ichigo and his allies are now friends of the Soul Society. But there is work to do.
Ichigo trains with the rogue Visoreds in Karakura Town to master his inner hollow, and just in time. Aizen is sending Arrancars, or unmasked hollows with swords, to attack Ichigo and his allies. Grimmjow and Ulquiorra are particularly deadly, and the latter abducts Orihime and drags her to Las Noches (Aizen's palace in Hueco Mundo). What comes next is a loose repeat of the Soul Society arc but in an entirely new world with a previously inconceivable enemy. Arrancars are strange mutant hybrids, and they are a deadly threat that no one saw coming. Ichigo and his allies do find Orihime, and four Captains arrive to help him. But it was all a ruse: these heroes are trapped in Hueco Mundo, and Aizen moves to invade Karakura Town with his army and create the Oken, or the key to the heavens.
Ichigo and his friends give it their all, and at last, Aizen's grand scheme is torn apart and he is captured. Ichigo loses his powers from sheer exhaustion, but there is another threat looming...
Return Of The Quincy
The Quincy were thought to be long dead. Not so: they have been hiding with their king (Yhwach) in a shadowy alternate reality, and now, they are ready to strike back against the Soul Reapers who defeated them 1,000 years ago. Ichigo, who has his powers back online, rushes to aid the Soul Society against the merciless Wandenreich assault. Captain-General Yamamoto loses his life to Yhwach, and Zangetsu is broken.
Now the plot is about vengeance and a clash of wills, where the Soul Reapers seek to maintain the flow of souls while the Quincy wants to create a world where life and death are blurred, thus erasing the soul-crushing fear of mortality itself. The stakes are even higher this time, and they are against an enemy thought long dead. Ichigo also learns more about his own ancestry, especially where his mother, Masaki Kurosaki, is concerned. Previous arcs hinted nothing of this, but now the truth is out. Masaki was a human Quincy, and Captain Isshin Shiba gave his life to save her from the poison of hollow powers. Yhwach is defeated at last, and Ichigo defies his Quincy heritage to crush the Wandenreich once and for all.
This story arc concludes the four-for-one saga, but it adds a pleasant twist: Ichigo and Orihime have married, and their son Kazui has the powers of a Soul Reaper, too. A new generation has been born.