Taiga Saejima is a central character in the story of Yakuza 4. In 1985, he belonged to a Third Tier family belonging to the massive Tokyo Yakuza alliance known as the Tojo Clan. Along with his blood brother, Goro Majima, he was given an order to assassinate the leader of a rival yakuza clan, the Ueno Seiwa. On the day of the assassination, Majima mysteriously did not show up, so Saejima proceeded without him, storming into the ramen shop where his target was eating, and nearly killing him, along with eighteen of his clan officers.
Twenty five years later, now a death row inmate awaiting execution for his crimes, he is transferred to a secret prison in Okinawa, Japan known only as Okinawa Penitentiary 2. It is there that he meets ex-Tojo clan lieutenant Goh Hamazaki, who is serving time for stabbing Yakuza protagonist Kiryu Kazuma the previous year. While in prison, Saejima learns from Hamazaki that the events of that day in 1985, were not as they appeared. Hamazaki hatches an escape plan to break out of the prison, and enlists the help of Saejima, who wishes to learn the truth of what happened on that day in 1985. The two escape the prison, but Hamazaki is wounded and separated from Saejima during the prison break.
Saejima washes up on the beach in front of Kiryu Kazuma's Sunshine Orphanage. Kiryu nurses him back to health, and assists him in returning to Kamurocho. With the police relentlessly searching for him, Saejima sets out on his quest to discover the truth behind the assassination in 1985.