Toguro Ototo is the younger brother of Toguro Ani, and lover of the psychic Genkai. During his youth he became world famous as a demon killer, something that brought young men from around the globe to train under him. However this was short lived as they were all slaughtered by a demon named Kairen while he was away to force him and his teammates into the Dark Tournament as the Tournament's wild card team. He then prepared for the Dark Tournament by retreating into the wilderness where he lived for 3 months while training, returning to his team the day before the Dark Tournament. Team Toguro eventually worked their way through to the Finals,where in the final match Toguro killed Kairen,and he and his brother utilized their wishes to become demons themselves. For the next 50 years the Toguro Brothers worked as hired guns and battled multiple demons such as Bui and Karasu sparing them to allow them to become stronger for a future rematch.
The Toguro Brothers eventually have a battle with Spirit Detective Yusuke Urameshi and his ally Kazuma Kuwabara, after the Brothers are hired by Tarukane to ensure the ice apparition Yukina continues crying for the valuable diamonds her tears form. This leads to a fight between the two teams, with the older Toguro Brother becoming weapons for his younger brothers fight, but eventually he falls to their teamwork. After everyone clears the Mansion they awaken revealing they threw the fight so their true employer Sakyo could collect bigger winnings,before Toguro murders Tarukane on Sakyoa's orders.Toguro then confronts Yusuke outside of his school forcing him to follow him before showing him 60% of his true power, leaving Yusuke completely terrified. He then threatens Yusuke into competing in the upcoming Dark Tournament,which Yusuke reluctantly accept with the two departing without a problem. He then meets with Kurama and Hiei informing them of their participation on Team Urameshi.
Upon Hanging Neck Island, Younger Toguro would frequently fight his team's battles on his own. While acting as the bodyguard for his employer Sakyo, defending him when the Tournament Committee learned of his plan to open a portal between Earth and the Demon World. This forces Toguro to murder the demon enforcers and the Tournament Committee themselves.Following this he skips his teams semi-final match to have a death match with the depowered Genki,culminating in him killing her. However he proves remorseful urging Koenma to care for her body so she could be revived after the tournament's end. Shortly after the final match of the tournament arrives with Toguro battling Yusuke, and quickly dominating the younger fighter in battle.However he refuses to strike a killing blow on several occasions as he felt Yusuke wasn't using his true power, however this ends when Genki possesses Pu, and instructs Toguro to murder a member of Team Urameshi to break down the emotional walls Yusuke has put up and draw out his true power. He then attacks Kuwabara, making Yusuke believe his best friend to be dead,unleashing his power.Their battle then reaches it's end where each uses the majority of their spirit energy, however Toguro exhausts his life force alongside it killing him and leaving his body a shriveled husk.
Upon his death he is brought to Spirit World where Koenme offers him a light sentence, that he refuses instead opting for 10,000 years in the deepest depths of hell.Upon his journey to the gates he is met by the spirit of a young Genki, who attempts to dissuade him from his self imposed punishment.But to no avail as he enters the gates as he leaves Genki with the message to watch after Yusuke, and about how beautiful their lives together could have been together.