A prominent figure in the state's history, Yaji used a religious revolution to finally solidify his family's grasp on Kano and its sub-kingdoms after centuries of strife.
All subsequent Kano Kings engaged in feuds with the pagan population but were unable to gain mastery over them.
In 1350, Yaji aided by Soninke Wangara scholars from Mali, relinquished the Hausa Animist Cult of Tsumbubura, and proclaimed Kano a Sultanate.
He violently crushed a subsequent rebellion by the animist cult at the Battle of Santolo, waging in the processes the first Islamic Jihad in Sudanic Africa.
He conquered the Kwararafa and the numerous Hausa kingdoms around Kano laying the seeds for Kanoan dominance in the Bilad as-Sudan.
His bad temper as a child earned him the epithet "Yaji", which is known today as a Hausa spice mix.
According to the Kano Chronicles, about forty Soninke Wangara scholars from Mali, led by Abdulrahman Zaite fully converted the King to the Islamic faith after which Yaji proclaimed himself a Sultan.
Yaji made Zaite Alkali (Qadi), Laual Muezzin, and Gurdamus his Liman (Imam).
According to the Kano Chronicle, the leader of the pagans was struck blind shortly afterwards and soon after all his acolytes involved in befouling the mosque.
For this reason he set his sights on conquering Santolo, the stronghold of the pagans in Kano because he believed every other town will follow him if he was able to succeed.
Yaji scored a crucial victory against the pagans in the Battle of Santolo, which would see him hold further successful conquest south of Kano.
This culminated in a confrontation with the Kwararafa, where its inhabitants were said to have deserted their land in fear, taking refuge on a hill in Tagara.
Yaji shared the same father and mother with Sarki Muhammad Bugaya which was unusual or Kanoan rulers in that era due to excess polygamy.
Yaji's actions were pivotal as they cleared the path for Kano's eventual supremacy among the Hausa states and in Sudanic Africa.
A mosque was built beneath the sacred tree facing east, and prayers were made at the five appointed times in it.
The Sarkin Gazarzawa was opposed to prayer, and when the Moslems after praying had gone home, he would come with his men and defile the whole mosque and cover it with filth.
The chief among his men were Jarumai Gobarra Dagga Samma, Jakafada Kulli, Ragumar Giwa, Makama Butache, Maidawaki Koamna, Berdi Sheggi, Sarki Zaura Gamati, Dan Buram Gantururu, Dan Maköo Dagazo, Galadima Tuntu and Sarkin Surdi Maguri.
Others were Gauji, Garoji, Tankarau, Kargagi, Karfasha, Kutunku Toro, Kampachi, Gorongiwa the Galadima, Zaki, Bamboli and others—altogether 60.
In the dead of night the Wongarawa went to Santolo together with Yaji and marched round the city and prayed till daybreak.
Kosa, the Sarki’s slave, said, “My lord, I will tell you the secrets of the enemy; there are 8 men inside the city and no one can pass the moat unless he kills them.” Famori said, “Do you know their names?” He said, “I know them.” So Famori said, “What are their names?” And Kosa replied, “The name of the greatest is Hambari, and after him Gwoshin Bauna, Kafiwuta, Gurgurra Karifi, Gandar Giwa, Hamburkin Toka, Zan Kaddakere and Gumbar Wakke.” Gwoji said, “If I see Hambari I will kill him, if Allah so wills.” At sunrise the Sarki returned to the attack on Santolo with black looks.
Hambari caught him by the throat and dragged him from his horse; but in vain, for Gwoji drew his knife, and ran him through, and so he died.
Gwoji entered the place of their god, with Kosa and Guragu, and found a bell, and two horns, a battle-axe and leg-irons.
Yaji stayed seven days in the town and destroyed the place of sacrifice, and after dismantling its wall and tree, returned to Kano.