Shinji Hirako is the former captain of the 5th Division, preceding his lieutenant Sōsuke Aizen. He distrusted Aizen from the day they met, and thus made him lieutenant so he could keep an eye on him. Because Shinji never socialized with Aizen, however, he was easily deceived by Aizen's actions, culminating to his conversion into a hollow. Shinji's character is somewhat comical, adding a bit of levity to situations that are otherwise serious. He seems to like annoying his associate, Hiyori Sarugaki, which usually earns him a slap from one of her sandals. He also appears to have a history of referring to cute girls he meets as his 'first love', complete with a deadpan look on his face despite the obvious lie (he apparently never did this with Hiyori, further annoying her). An early design of Shinji can be seen in the first chapter's cover art, making it clear he was planned well before his introduction. During several points in the anime, Shinji's outfit is depicted to look like Lupin the III, likely as a homage on the part of the animators.
Shinji's hollow mask resembles a pharaoh's mask. Shinji is quite skilled with his hollow powers, using a single cero blast to easily overwhelm Grimmjow Jeagerjaques. The video games also depict him being able to split the cero blasts into a pyramid shaped attack.
Shinji's zanpakutō, Sakanade (逆撫) has the power of creating an inverted world. The power is an optical illusion which is caused by the scent the sword gives off upon its release. It inverts an opponent's sense of direction causing the directions of up and down, left and right as well as forward and backward becoming the opposite. It is not just the sense of direction that is changed; the opponent's eyesight and where they get cut is reversed as well.
In its sealed form, Sakanade resembles a normal katana with red hilt and sheath whereas upon its release, its hilt becomes a large ring which Shinji places his hand in the middle of allowing him to freely control its movement without physically holding onto it if he so chooses. The ring is attached to a normal sword hilt with a normal rectangular hand guard. The first few inches of the blade are covered by as extension of the hand guard. Sakanade's blade is straight and slim with the tip ending in a slanted razor-like edge instead of being tapered to a point. There are five holes along the swords length.
He has a tattoo on his tongue, as seen in episode 142.
(Source: Bleach official character book II)
