[6] In 1564 at what appears to have been an early manhood ceremony, Kotsumaru took the name Terumoto (Teru coming from the shogun, Ashikaga Yoshiteru) and assumed command.

[citation needed] After Terumoto had put down the rebellion led by Ouchi Teruhiro, he set out with a large army from Yoshida Koriyama Castle together with Motoharu and Takakage to defeat the remnants of the Amago clan forces.

[12] When Motonari died in 1571, Terumoto inherited an enormous kingdom that stretched from Buzen on Kyushu to the borders of Harima and Bizen, a powerful navy (at the time Japan's finest), and the support of two gifted uncles Kobayakawa Takakage and Kikkawa Motoharu.

In December 1573, Nobunaga acknowledged Uragami Munekage, a key figure in anti-Mōri forces, with control over Bizen, Mimasaka, and Harima.

In 1576, First Battle of Kizugawaguchi Nobunaga's 'admiral', Kuki Yoshitaka, had cut the Honganji's sea-lanes and sat in blockade off the coast.

Terumoto ordered his fleet, commanded by Murakami Takeyoshi, to make for the waters off Settsu and, once there, the navy inflicted an embarrassing defeat on Kuki and opened the Honganji's supply lines.

After Hongan-ji surrender, this allowed Nobunaga to concentrate on the Mōri and he sent two sizable contingents westward into the Chugoku region.

Hashiba Hideyoshi was to march along the southern portion of the arm (the Sanyodo) while Akechi Mitsuhide moved into the upper provinces (the Sanindo).

[16] Shimizu Muneharu (a former Mimura retainer) defended Takamatsu stoutly, but its loss would all but open the way into Bingo and Aki, the Mōri homeland.

Hideyoshi knew that Takamatsu would be a tough nut to crack and that heavy losses would only benefit the Mōri, so he resorted to a stratagem.

[1] Terumoto sent the 'Two Rivers' (Kobayakawa and Kikkawa) to lead troops for Hideyoshi in his Invasion of Shikoku (1585)[17] and Kyushu Campaign (1587).

When Hideyoshi invaded Korea in 1592, Terumoto himself led the "7th Division" with 30,000 troops there, although much of his time seems to have been taken up fighting Korean partisans at Gyeongsang Province.

Terumoto was at Osaka Castle defending Toyotomi Hideyori at the time and later surrendered to Ieyasu soon after Mitsunari defeat at Sekigahara.

Ieyasu reduced Terumoto's domains, leaving him only Nagato and Suō Provinces, worth 369,000 koku in total.

[citation needed] In August 1614, tensions between the Edo Shogunate and the Toyotomi clan rose due to the issue of the inscription on the bell of the Great Buddha Hall of the Hokoji Temple.

[19] Terumoto instead rather supporting the Tokugawa shogunate, as on November 3, Terumoto ordered his vassals Mōri Motochikazu and Motoyuki Sugimori, who were in charge of Mōri Hidemoto's absence, to send half of the troops east if Hidemoto asked them to march out to aid the shogunate fought the Toyotomi, while the remaining half, including Sugimori, Motoyoshi Nishi, and Shichirobei Misawa, were to stay in Chofu as caretakers, and to retreat to Hagi if something happened that would make it impossible to maintain Chofu.

[21] During the Summer Siege of Osaka, some of the former vassals of the Mōri clan, such as Naito Motomori (Sano Michika), Karasuda Tsuji, Koda Masatane, and Kasai Shigemasa, joined the Toyotomi side.

He was interrogated by Yagyū Munenori, an Ometsuke official in charge of the investigation, about the suspicion that Motomori had entered Osaka Castle on Terumoto's orders, but Motomori claimed that he had entered the castle on his own initiative, and committed suicide on the 21st, which resulted in the suspicion against the Mōri clan being dropped.