Tanaka was a member of Dojima Family and a former lieutenant of Nishiki Family.
16 year old Shinji Tanaka was a member of a biker gang. He bears a resentment toward yakuza after loan sharks took advantage of his father's money issues, tearing his family apart. After separating from his father, he sought to make money by mugging yakuza.
He appears as an opponent in Kiryu's substory No. 20, wielding an iron pipe. After being beaten, Shinji is sold out by a member of his gang to the Jinsei family, and depends on Kiryu to save him. After having a talk with Kiryu, Shinji aspires to follow, and be just like, Kazuma Kiryu.
- "A member of the Dojima Family, an affiliate of the Tojo Clan. His full name is Shinji Tanaka. He joined the Dojima Family and became Kazuma's loyal subordinate. He admires and respects Kazuma. He is still very 'young' and makes a lot of mistakes."
Shinji starts as a Dojima Family member working under Kiryu. After the dissolution of the Dojima Family, Shinji joins Nishiki's Family becoming a Lieutenant. While many of Kiryu's old friends forgot about him while he was in prison, Shinji did not. After Kiryu returns from prison, Shinji shows where his true loyalties lie by helping out Kiryu and Shintaro Fuma (Kazama).
When Fuma gets shot in Chapter 3, Shinji harbours him from Nishiki and the others that are after him.
Later, in Chapter 10 Shinji helps Reina escape from Nishiki and this whole chapter involves finding Shinji and trying to save him from hoards of Nishiki Family members.
At the end of Chapter 10, Shinji dies from gun wounds most likely inflicted by Arase's subordinate Mochizuki