100 hundred years before the current Bleach time line (Turn back the pendulum arc) Shinji Hirako serves as the captain of the 5th division. In this time a younger and seemingly innocent Aizen serves as his lieutenant. Though he is a captain.....Shinji would often show behavior that is childish and immature for a man of his age and ranking. This is especially seen during his confrontations with the 12th division lieutenant Hiyori Sarugaki. Shinji often being attacked by her in random and numerous situations, and though his own lieutenant believes his captain should be more responsible he never is. Though Aizen was his subordinate....Shinji did not like, nor did he trust Aizen. He was not fooled by his seemingly innocent facade, and knew there was more to Aizen than meets the eye. At this time Shinji would also build somewhat of friendship with Kisuke Urahara who had just been promoted. At times giving advice that showed the wisdom worthy of a captain.
It was during this time, that Aizen first began experimenting with hollowfication. Which led to a number of mysterious disappearances around soul society. Though Aizen would never be caught for the act until 100 years later. These mysterious disappearances were being investigated by the 9th division including future vizards. Kensei Muguruma and Mashiro Kuna. Whom were the captain and lieutenant of the 9th division at the time. It was later learned that the 9th division themselves had mysteriously disappeared. The act forced Yamamoto to act quickly and efficiently and so he decided to send out a group to investigate. Shinji was one of those along with the captains and lieutenants who would become the vizards. Shinji arrives just in time to save Hiyori, but immediately is forced into battle with the others against Kensei and Mashiro who have just become hollows. The fight is incredibly tough. Especially against a friend but eventually Kensei is subdued. Though it seems everything was okay, Hiyori transformed and attacked Shinji. Before the others could react they were attacked by Kaname Tosen, who was revealed to have betrayed Kensei.
It was then that Aizen appeared along with Ichimaru Gin, and finally revealed himself to his captain as the mastermind behind all the disappearances and experiments. Though Shinji himself had always suspected Aizen. Though it was right and smart of Shinji to choose Aizen and keep him under watch, he made some fatal errors which allowed Aizen to deceive Shinji. Not once did he attempt to get close to his lieutenant, so he did not get to know the man and his characteristics. It was because of this that Shinji had failed to realize that following for the past month was someone else. Agitated and angry at Aizen. Shinji undergoes his own hollow transformation. Aizen then decides to attack and kill Shinji but he is saved with the sudden appearance of Kisuke and Tessai who fend Aizen and his subordinates away. Shinji along with he others try to have the process reversed but the damage is set. So instead Kisuke gives them all untraceable gigai. So they can hide in the human world, as staying in soul society would have led to their execution.
Shinji Hirako is now the current leader of the Vizard. He was originally the Captain of the 5th Division but became a Vizard under unknown circumstances. He first appeared when Ichigo returned home from Soul Society. He came to persuade Ichigo to join the Vizard but Ichigo turned him down. Later Ichigo came back and asked him to train him. To accomplish this task, Shinji knocks Ichigo unconscious so he can face his inner hollow out to battle on common ground. After awakening his powers Ichigo left because the Arrancar were attacking Karakura Town. Ichigo was about to be defeated by Grimjow until Shinji came and saved Ichigo. Shinji was almost about to finish him but Ulquiorra Schiffer stopped their fight and told Grimjow to return to Heuco Mondo.
Vizard vs Espada
When things look grim for the shinigami, Shinji arrives with the Vizards to save the day. While his allies are busy saving Toshiro, Soifon, and others. Shinji briefly chats with captain Yamamoto before turning his full attention to Aizen. Before leaving Shinji reveals caring only to help Ichigo and not the Shinigami. Shinji goes to cut Aizen down but Tosen intervenes. The two spare for a moment when Komamura steps in. Komamura takes it upon himself to ally the shinigami with the vizards.
Shinji's Zanpakuto is called Sakanade and its release command is Collapse. Its Shikai form has a large ring at the bottom of the hilt, with which Shinji swings his sword around. The blade also has five holes in it which may have something to do with its power. Sakanade's power is to create optical illusions through a smell it produces. It is believed that the smell is released when Shinji spins his sword with its ring. The illusion is called an Inverted World by Shinji. Here, the opponent's sense of direction is reversed. Forwards becomes backwards, left become right, and up become down. Shinji considers his Zanpakuto's power a trump card due to its nature and the fact that fighters will act on reflex even if they're used to its power. It has also proven to be very useful in group battles, as Shinji could use it to fool an opponent when a teammate is attacking.
Earlier in the series, Shinji mentioned that he likes to do things backwards. His first appearance was also standing upside down. These things could be seen as a foreshadowing to his Zanpakuto's power.
As a former Captain Shinji is capable of Bankai, but what his Bankai is has not yet been revealed but it is likely that it will follow his reverse theme or personality in some manner.
Shinji's mask strongly resembles a pharaoh's mask with a short flowing hood down the the back of has neck. When he donning his mask his cero blast turns black and irises gray. While wearing the mask his Shinji's hollow powers supplement his shinigami powers giving him a vast increase in both strength and speed
Cero: Shinji's gathers energy that is displayed in a horizontal line at his fist. He then releases a crimson cero with an extremely wide arc and devastating force.