Chōsokabe Motochika (長宗我部 元親; 1539 – July 11, 1599) was a daimyō in Japanese Sengoku-period.
He was the 21st chief of the Chōsokabe clan of Tosa Province (present-day Kōchi Prefecture), the ruler of Shikoku region.
He was the son and heir of Chōsokabe Kunichika and his mother was a daughter of the Saitō clan of Mino Province. His childhood name was Yasaburō (弥三郎). He is said to have been born in Okō Castle in the Nagaoka district of Tosa. Motochika was a tall, fair-skinned, but quiet. His father, Kunichika, was said to have fretted about the boy's gentle nature (he seems to have been nicknamed Himewako, or 'Little Princess'); Kunichika's worries evaporated when Motochika later proved himself a skilled and brave warrior. When Motochika came of age, his father had already begun to draw away from the Ichijō family, and Motochika would carry on his work.
In 1560, at the Battle of Tonomoto, Chōsokabe Kunichika captured Nagahama castle from the Motoyama clan. In response to this, Motoyama Shigetoki departed Asakura castle with 2,500 men to take the castle back. Kunichika intercepted him with 1,000 troops near Nagahama castle. This battle is noted for being Chōsokabe Motochika's first battle, in which he fought bravely, greatly impressing his father and his retainers.
In 1562, Chōsokabe Motochika attacked Asakura castle defeated Motoyama Shigetoki and by forming alliances with local families, Motochika was able to build his power base on the Kōchi plain.
In 1569, while being careful to remain ostensibly loyal to the Ichijō family over the next few years, Motochika's power grew to the extent that he was strong enough to march on the rival Aki clan of east Tosa with 7,000 men, He defeated Aki Kunitora at Battle of Yanagare, then went on to take Aki Castle.
In the course of the decade he was awarded the court rank Ministry of Imperial Household (Kunai shō) and was sufficiently confident after the reduction of Aki to finally turn on the Ichijō family.
In 1573, while still lord of the Hata district of Tosa, Ichijō Kanesada was unpopular and had already suffered the defection of a number of important retainers. Seizing the opportunity, Motochika with his brother Kōsokabe Chikayasu, wasted no time in marching to attack on the Ichijō's headquarters at Nakamura, and Kanesada fled to Bungo, defeated.
In 1575, at the Battle of Shimantogawa (Battle of Watarigawa), he defeated the Ichijo family.
Following his conquest of Tosa, Motochika turned north and prepared for an invasion of Iyo province. The lord of that province was Kōno Michinao, a daimyo who had once been driven from his domain by the Utsunomiya clan, returning only with the assistance of the powerful Mōri clan. However, it was unlikely that Kōno could count on that sort of help again as the Mōri were embroiled in a war with Oda Nobunaga. Nonetheless, Chōsokabe's campaign in Iyo did not go off without a hitch.
In 1579, a 7,000 men Chōsokabe army, commanded by Kumu Yorinobu, met the forces of Kōno Michinao, led by Doi Kiyonaga at the Battle of Mimaomote. In the ensuing battle, Kumu Yorinobu was killed and his army defeated, though the loss proved little more than an unfortunate delay. The next year, Motochika led some 30,000 men into Iyo Province, and forced Kōno Michinao to flee to Bungo province.
In 1580, Oda Nobunaga disapproved of Motochika's conquest of Shikoku, despite being allied with them. This commotion started from Motochika's effort to respond the Miyoshi clan's threat, by strengthened ties not only with Nobunaga but also with Mōri Terumoto to isolate the Miyoshi clan diolomatically. However, Motochika did not change his policy even after Nobunaga began a full-scale invasion of Chugoku Region against the Mōri clan, which caused Nobunaga to distrust grow suspicious about Motochika's allegiance. However, historian
Yoshihiro Kawashima stated the relationship between the Mōri and Chosokabe clans had already broken down by the time the Mōri and Miyoshi clans made peace in 1575, and that the alliance between the Chosokabe and the Sanuki Kagawa clan (the adoption of Kagawa Chikazu) itself was the result of the shared interests of the two clans, who were pro-Oda and under threat from both the Mōri and Miyoshi clans. Regardless the reason, Nobunaga only allowed Motochika to possess Tosa Province and the southern half of Awa Province and submit to him unconditionally after the provocation from Miyoshi Yasunaga who just recently submitted to Nobunaga.
With little interference from either the Mōri or the Ōtomo, Chōsokabe was free to press onwards, and in 1582, he stepped up ongoing raids into Awa province and defeated Sogō Masayasu and the Miyoshi clan at the Battle of Nakatomigawa.
Later, Motochika advanced to Sanuki province and defeated Sengoku Hidehisa at Battle of Hiketa.
By 1583, Chōsokabe Motochika had controlled Tosa Province, Iyo and subdued both Awa and Sanuki.
Over the ensuing decade, he extended his power to all of Shikoku island, making Motochika's dream of ruling all of Shikoku a reality.
After unifying Tosa, he formed an alliance with Oda Nobunaga, who was promoting the unification project in the central government, through kinship with his wife.