After Tou conquered Han, Zhao was struck by two natural disasters (an earthquake and a severe famine) In 229 BC, Qin took advantage of the situation to launch a pincer attack from the north and south on Kantan led by Ousen, Yotanwa and a third general i don't know (Qiang Hui) but they got stalemated by an army led by Riboku/Shibashou. Unable to advance further, the Qin army bribed Guo Kai (Kaku Kai, a high ranked Zhao minister):
To make King of Zhao suspects and distrusts Li Mu (Riboku). The king doubted Li Mu's loyalty and ordered Li Mu to hand over his authority to his deputies, executing him in the following year (228 BC). Without Riboku hindering their way, Qin forces attacked and conquered several cities before conquering Kantan.