Shinichiro Tamaki began as a member of a Japanese resistance cell before joining the Black Knights. Initially skeptical of Zero's leadership and motives, he evolved into one of Zero's most ardent supporters. His personality was marked by impulsiveness and recklessness, frequently leading to poor combat decisions, like ordering the execution of Ashford Academy students against Zero's orders. This rashness extended to piloting; he often ejected early from Knightmare Frames and was statistically rated among the Black Knights' least effective combat assets. Despite these flaws, he displayed fierce loyalty, maintaining belief in Zero's return even after a year imprisoned following the failed Black Rebellion, despite widespread reports of Zero's death.

During the Black Knights' restructuring, his role changed from leading the second special squadron to becoming the Internal Cleaning Supporter, a position he resented. He often complained about his lack of significant responsibilities and expressed irritation at C.C.'s unofficial presence, insinuating her involvement stemmed only from a personal relationship with Zero. This dynamic later evolved into mutual banter. His loyalty faced its ultimate test when Zero's true identity as Lelouch vi Britannia was revealed. Tamaki reacted with intense betrayal, initially refusing to accept it but later turning vehemently against Lelouch, even threatening Kallen Kouzuki for her hesitation.

In the spin-off manga *Suzaku of the Counterattack*, Tamaki acted as a minor antagonist. Disregarding Kallen's objections, he led rogue Black Knights in a failed attempt to kidnap Lenard Lubie to uncover Lancelot secrets. This operation resulted in Lenard's death, damaged the Black Knights' reputation, and indirectly encouraged further reckless actions causing civilian casualties.

Following Lelouch's death and the Zero Requiem, Tamaki transitioned to civilian life. He opened a successful bistro named Cafe Zero in honor of the fallen leader, displaying unexpected business acumen. He attended Ohgi's wedding, celebrating with former comrades. During *Code Geass: Lelouch of the Resurrection*, Tamaki traveled to Zilkhstan to aid Zero. Shocked to discover Lelouch, revived by C.C., was alive, he quickly pledged full support and defended Zero against Cornelia li Britannia. Partnered with Ohgi during Nunnally vi Britannia's rescue, they initially succeeded but were ambushed by Shamna. They escaped, commandeered a Knightmare Frame to contact Zero, and contributed to the mission's success, later reflecting on their actions over drinks with Ohgi. His post-series life centered on operating Cafe Zero, often seen with associates like Kento Sugiyama, Kallen Kouzuki, and Benio.