After Nobunaga's death at Honnoji, Mitsuhide requests for the Tsutsui clan to aid him at Yamazaki. Sakon, a former Takeda general who resided with the Tsutsui at the time, convinces his master to instead side with the more capable Hideyoshi. During the conflict, Mitsunari and Sakon keep track of the other's promise of talent. Hideyoshi becomes the land's de facto leader after he defeats other Oda generals. By this time, Sakon was angered by his lord and wandered the land for indulgence. Mitsunari finds him and, once the younger man states that he wants his services as his equal, Sakon agrees to serve him. He aids the land's unification by suppressing Kyushu and by partaking in the western siege at Odawara Castle.
Hideyoshi soon dies and the land is split between factions lead by Mitsunari and Ieyasu. Facing Ieyasu's vast army, Sakon requests permission for an ambush to stunt the enemy march and traps select portions of the Eastern army at Kusegawa. Cutting back some of Ieyasu's drive, Mitsunari moves to Sekigahara. Although Sakon rationalizes that Mitsunari's plan won't succeed, he nevertheless fights by his lord's side. After their victory, Sakon replies that he doesn't care about a reward as he just wanted to serve a virtuous lord. As he speeds off on his steed, Mitsunari considers Sakon to be his friend.
In Samurai Warriors 3, Sakon begins his story in a manner similar to his previous dream stage. With Ieyasu's escape in the end, Shingen is unable to secure a decisive victory against Ieyasu in his following campaigns and his abrupt death leads to eventual demise of the Takeda family. Seeking a new master, Sakon joins Hideyoshi's side at Komaki-Nagakute and meets Kiyomasa, Masanori and Mitsunari. During the battle, the trio's words has him reflect on Hideyoshi's character and, though he considers joining Hideyoshi, he is more impressed by Mitsunari's will to win. Joining Mitsunari at Oshi Castle, he agrees to help the youth's dream of protecting the Toyotomi's future with his friends. Upon achieving victory, Sakon finally accepts Mitsunari as his real master.
Soon after, Hideyoshi dies due to illness and Mitsunari is abandoned by his friends. At odds with the larger Ieyasu army and devastated by the loss, Mitsunari's army suffers from low morale. To boost the spirits of Mitsunari and the men, Sakon leads an attack at Kusegawa to defeat Tadakatsu. Their victory is enough to cement Mitsunari's resolve to win and they proceed to Sekigahara. Although Kiyomasa's presence in the Eastern army once again weakens his master's nerve, Sakon defeats him to lead the army to a decisive victory and they rout the Eastern army. Kiyomasa's defeat dazes Mitsunari into a witless stupor and he loses the will to pursue Ieyasu's army. To raise his master's spirit, he hauls the young man onto his horse, attracts Masanori's attention to follow them, and speeds towards Kiyomasa. Although the latter looks as though he is dead, he awakens when Mitsunari hurries to his side and a crying Masanori hugs both of them. Seeing the trio reunited is enough for Sakon to smile.