Bleach Shirokuro Chronicles

The Bleach Shirokuro Chronicles was the successor to the classical Bleach series that takes place roughly twenty years after the end of the The Thousand-Year Blood War arc, continuing the storyline of Bleach into the next generation, and introducing Ichigo Kurosaki's son as the main protagonist.

Plot
Spending two decades coiling in hatred and madness - a lifetimes worth within Muken, the 8th and lowest level of the underground prison, the Hogyoku seems to have died and its power gone despite Aizen's continued Immortality.

In the meantime, Kisuke Urahara discovers a young man with hungry eyes and no memory of his past life, taking him under his wing he named the youth Akirameru and is curious on how he can exist in the physical and spiritual world at exactly the same time yet is neither a Quincy or a Fullbringer.

Soon the Kurosaki family get involved in Akira's life when unique entities called Henkei that were born from the remains of once former enemies, led by the Four Kings of Eternity, come to Karakura Town seeking a "unique Youth" provoking Soul Society to plan an intervention.

Trivia

 * Shirokuro means "black and white", which hints that the story probably relates to the greys often found between the two colours.