KEY REVELATIONS
Every major plot twist, secret, and revelation, in episode order. Spoilers ahead.
Grand Fisher killed Ichigo's mother Masaki by luring her with his decoy lure
Quincy were a spiritual race who destroyed Hollows entirely (vs Shinigami who purify). Soul Society exterminated them to preserve the balance of souls.
AIZEN'S BETRAYAL: Aizen faked his death with Kyōka Suigetsu's perfect hypnosis, which controls all 5 senses. He, Gin, and Tōsen defect to Hueco Mundo with the Hōgyoku.
Aizen's plan was to extract the Hōgyoku Urahara hid inside Rukia's soul. The Hōgyoku dissolves the boundary between Shinigami and Hollow.
Visored are former captains/lieutenants Hollowfied by Aizen 100 years ago. They control their Hollow masks.
Isshin Kurosaki is a Shinigami, kills Arrancar Grand Fisher in one blow. Ryūken Ishida is a Quincy.
110 years ago, Aizen experimented on Shinigami to create Hollowfication. Urahara and Tessai were framed and exiled.
Ulquiorra has Segunda Etapa (second release), unknown even to Aizen. Only Espada with this ability.
Gin's true motivation revealed, he always planned to kill Aizen. He joined Aizen solely to find a way to kill him because Aizen stole a piece of Rangiku's soul as a child.
Aizen reveals he has been manipulating Ichigo's entire life, every battle, every opponent, to make him the perfect specimen
Final Getsuga Tenshō (Mugetsu). Ichigo becomes Getsuga itself for one ultimate attack, then loses all Shinigami powers
Yhwach is the Father of all Quincy, born without senses, gained power by sharing pieces of his soul. His son, the Soul King.
Unohana is the original Kenpachi. Yachiru Unohana, the most diabolical criminal in Soul Society's history. She sealed her own power.
Old Man Zangetsu was actually a manifestation of Yhwach (Ichigo's Quincy powers) suppressing his Shinigami/Hollow powers. The Inner Hollow was his TRUE Zanpakutō spirit.
Ichigo's heritage: Shinigami father (Isshin Shiba, former 10th Division Captain), pure-blood Quincy mother (Masaki Kurosaki), with Hollow taint from White
Ichigo's true Zangetsu is a dual blade, one Shinigami/Hollow, one Quincy, reforged by Ōetsu Nimaiya of Squad Zero
The Soul King was the original powerful being, mutilated and sealed by the original Shinigami to stabilize the three worlds. He is Yhwach's father.
Yhwach's The Almighty can see and alter all possible futures. The only counter is the Still Silver (Quincy blood that has been touched by death).