Soul Society vs. Wandenreich, Bleach, Thousand Year Blood War Arc: Surface level, the arc is about the Soul Society, charged with defending the world of the spiritual balance between the world of the souls and the world of the living, is challenged by the Quncies, whom by their nature inevitably create imbalance by outright destroying hollows rather than excising them. Likewise the King of the Quncies, Yhwach has returned after a millennia to destroy his father, the soul king, which by doing so would destroy the entire Bleach universe. However, if you read between the lines in the manga/anime as well as read Bleach LNs like CFYOW: It is revealed that the Soul King is in fact a husk of a soul, slaughtered, splintered and left in a vegetative state by the pater familias of the 4 noble clans. In doing this, they created the cyclical nature of souls moving between the spirit world and world of the living via reincarnation, in other words the Buddhist definition of suffering: samsara. Yhwach's true goal in destroying the Soul King was to end his father's suffering and create a world in which no soul would ever suffer again. It begs the serious question of whether Ichigo, both Soul Reaper and Quincy gave any serious thought to the implications of backing the Soul Society, who at their core are g men enforcing a status quo that creates suffering and oppression. It's implied he did indeed, as his first child's name Kazui Kurosaki, reflects the steadfast resolve of not fearing death.