**Spoiler alert**  
Mt. Leikaku is the name of the mountain before a known city to the east in Konan Country. On that mountain resides a notorious group of bandits once lead by the former leader Hakurou.
In this section, I elaborated on how and why Tasuki became a member of the Mt. Leikaku bandits. A lot of the information found in this section will contain spoilers for those who haven't seen the entire series.  For others, it may contain some information on Tasuki, which was never revealed even after watching all of Fushigi Yuugi.

Why did he leave home?

Tasuki grew up with his mother, father and five older sisters. His dad never had much influence in his life and I'm not sure if he ever looked up to him. He was almost invisible around the company of his mother and older siblings. A slave to their everyday routines, succumbing to everything asked. Tasuki, especially, was subjected to doing all the chores around the house. In his eyes, his taskmaster sisters took advantage of him and after time, it left a negative impression in his mind and heart.  He brewed a hate towards women, which drew him away from females completely. It was at the age of fifteen when he decided to run away and have a life of his own without his family's interference or the resolve of women on a hold. He headed out to the city to the east where he had to cross Mt. Leikaku before getting to his destination. It was there he met Hakurou, the leader of the Mt. Leikaku bandits.

Meeting Hakurou

On his journey to the city, Tasuki encountered a group of bandits who cornered him while going up the mountain. He tried to put up a resistance but they successfully managed to strip him of all his clothing and money.  That was when Hakurou made his entrance, impressing Tasuki with his confidence, fearlessness and mannerisms.  He drove away the rival bandits returning to Tasuki all of his belongings. Even though Tasuki considered being a bandit a dirty occupation, something about the young leader really excited him. From then, he was really persistent in being granted acceptance to his group.  He had already perceived him as a hero. Moved by his determination, Hakurou finally accepted him in Mt. Leikaku bequeathing him with the name Genrou.

Genrou, the nickname 

Genrou means "Phantasm Wolf" and there is a reason behind Hakurou bequeathing Tasuki with that name.Tasuki hadn't gained acceptance into the Mt. Leikaku bandits on the first request. Hakurou had dismissed him and told him to return home that night.  But Tasuki, with determination, had infiltrated the Mt. Leikaku stronghold. He managed to arrive there before Hakurou using the animal path through the mountain, which was three times longer than the human path, not to mention being more dangerous. Hakurou considered the feat to be an act of a phantom. Tasuki's speed and fangs also gained him the comparison to a wolf.  Hence, the name "Phantasm Wolf".

Kouji  Rivalry to Friendship

Tasuki was placed under Kouji's wing at the dawn of his acceptance from Hakurou. Kouji, however, wasn't pleased with the decision the leader made.  If I analyze things further, I would infer that he was a bit jealous. He had a tendency to punch and slap Tasuki a lot. He pushed him around but Tasuki didn't seem to mind it one bit, or maybe he just knew how to mask his emotions, or maybe he just took a liking to him. Being in each other's company over time soon turned things around though. They soon became the best of friends. They were inseparable. The most time they spent apart was probably when Tasuki decided to join Miaka and the other Suzaku Seishi on their quest to summon Suzaku.