Background
Sha Jien from Gojyo's Memory
Originally named Sha Jien, he lived with this youkai parents. His father then took a human mistress and Sha Gojyo was conceived through the affair. After his half-brother's birth, his father and the mistress died. It is unknown whether or not these deaths were related. In the end, Gojyo was taken in by Jien and his mother. The brotherly bond between Jien and Gojyo was strong and they cared deeply about one another, but the same could not be said for Jien's mother.
She was driven mad over time and she started to physically and verbally abuse Gojyo as an outlet for her frustration and sadness. Jien did his best to sedate and his mother, even going to far as to take his father's place in her bed. Meanwhile, Gojyo began to blame himself for his mother's tears and the strained relationships in the family.
The weapon used to Kill Gojyo's mother varies between a Sword and a club.
One day she lost it completely, attacking Gojyo with the intent to kill. She scratched at his face with her demonic claws and left the scars that are visible to this day. As she cornered him, Gojyo had resigned himself to his death and thought if it could stop his mother from experiencing so much pain, he wouldn't mind dying. Jien refused to let that happen and intervened by killing his mother before she could do the same to Gojyo. But in the end, Jien could not take what he had done and abandoned Gojyo. Roughly six years before the beginning of the manga, Jien was taken in by Kougaiji.
Present
Saiyuki
When he entered Kougaiji's services, he relinquished the name Sha Jien and took up the name Dokugakuji. He was still in Kougaiji's services when he was unintentionally reunited with Gojyo again--On the battlefield. Gojyo was part of the infamous Sanzo Ikkou. The brothers exchanged witty banter and each stated that they had both chosen their paths and weren't planning on turning back. The reunion ended after the two groups temporarily banded together to defeat a gaint Shikigami that was attacking a village.
Dokugakuji returned with Kougaiji, his sister Lirin, and Yaone to Houtou Castle, their home. Lady Gyokumen Koushu, Kougaiji's step mother told Kougaiji to not confront the Sanzo Ikkou, but to focus his energies on finding the other remaining 'Heaven and Earth Scriptures'. Dokugaukiji and the others were upset with the change of orders, but did as they were told.
Eventually Dokugakuji heard about a scripture that was in possession of a scorpion demon in the desert that had eaten the Sanzo Priest that was governed with protecting it. The two of them set out to find it, but not before having a run in with one of the leading scientist working on the revival project to awaken Gyumaoh, Kougaiji's father. The scientist, Dr. Ni, gave Kougaiji a warning before they left about hold what you cherish most close to you. He also pushed some of Dokugakuji's buttons, bringing up his younger brothers and Gojyo's half-demonic/half-human lineage.
Kougaiji and Dokugakuji in the desert looking for the Uten Sutra
The two made it to the desert only to find that the scorpions demon, Ren ri, was dead and he castle under the sand buried, all the work of the Sanzo-ikkou. But the Sanzo party had not made it out unscathed and Genjo Sanzo, their leader, was greatly injured. Son Goku, another member of the Sanzo-ikkou asked Kougaiji for help. Kaougaiji made a reckless deal with him that if Goku could kill him, Kougaiji would give him one of their flying dragons. Dokugakuji tried to stop him, but Kougaiji insisted. Goku, who saw few opsions given Sanzo's state, agree and took off his Demon limiter taking his true form, Seiten Taisei.
Seiten Taisei beat Kougaiji to a bloody pulp and might had killed him if Dokugakuji had not stepped in. But the demonic teenager defeated Dokugakuji quickly as well. After Seiten Taisei was taken out by a barely conscious Sanzo, Dokugakuji retreated taking Kougaiji with him, claiming that he could never forgive the Sanzo-ikkou for this.
Back home, Dokugakuji searched for Yaone. Kougaiji was in need of medical care immediately. Unable to find her, Dr. Ni offered his services. With little options, Dokugakuji handed Kougaiji over to the mad scientist. Later Dokugakuji learned from Yaone that they had taken Lirin away to experiment on her. By then it was too late and the scientist had already messed with Kougaiji's head. After taking a few more painful jabs on Dokugakuji, Dr. Ni returned their prince to them, no longer the man he was before.
Saiyuki Reload
Dokugakuji blamed himself for not being able to protect yet another person that he saw as his "little brother". Kougaiji was commanded to find the Sanzo-ikkou again and this time annihilate them. Dokugakuji and Yaone followed after him, but lost him temporarily. They ran into the Sanzo-ikkou while looking for kougaiji. They kind of rescued the three remaining members from a river, only to be later confronted by a hired assassin named Zakuro who trapped the Sanzo-ikkou in an illusion. Zakuro tortured Gojyo to prove a point to Dokugakuji that the Sanzo party were their enemies.
Dokugakuji and Yaone protecting Kougaiji from the Sanzo party
When Sanzo broke out of the illusion himself, they all went looking for Kougaiji who was already fighting in the fourth member of the Sanzo-ikkou, Goku. Goku, tired from fighting a small army of demons before Kougaiji showed up, passed out when his teammates arrived. Gojyo, Hakkai, and Sanzo picked up where their monkey had left off.
When Dokugakuji and Yaone tried to step in Kougaiji threatened that if they got in his way, he would kill them. The two stood back watching until they couldn't take it anymore and step into to protect their prince. This was the first thing to crack the control that the Lady Gyokumen. When Dokugakuji was in danger, Kougaiji finally snapped out of it and returned to himself. The three of them returned to Houtou Castle and rescued Lirin. The four of them are currently training, determined to beat the Sanzo-ikkou under their own terms next time they meet.
Saiyuki Reload Blast
The next time we see Dokugakuji is with Kougaiji as they are sent to attack and invade Sharak Sanzo 's temple. The two split up with Kougaiji running into Sanzo and Dokugakuji taking on Hassan. During the fight, he can sense the demon prince is in trouble and runs to his aid, shielding him from a devastating blast from the war god bent on destroying all Youkai, Nataku. Dokugakuji pays the ultimate price for his sacrifice as Kougaiji cries out in despair.