Editing Tokugawa Ieyasu (section)

=== Service under Imagawa clan ===
{{Main|Siege of Marune|Battle of Okehazama|Siege of Kaminogo Castle}}

In 1556, Takechiyo officially came of age, with Imagawa Yoshimoto presiding over his ''[[genpuku]]'' ceremony. Following tradition, he changed his name from Matsudaira Takechiyo to {{Nihongo|'''Matsudaira Jirōsaburō Motonobu'''|松平 次郎三郎 元信}}. He was also briefly allowed to visit [[Okazaki Castle|Okazaki]] to pay his respects to the tomb of his father, and receive the homage of his nominal retainers, led by the ''[[karō]]'' [[Torii Tadayoshi]].<ref name="Turnbull-I"/>

One year later, at the age of 15 (according to [[East Asian age reckoning]]), he married his first wife, [[Lady Tsukiyama]], a relative of Imagawa Yoshimoto, and changed his name again to {{Nihongo|'''Matsudaira Kurandonosuke Motoyasu'''|松平 蔵人佐 元康}}. A year later, their son, [[Matsudaira Nobuyasu]], was born. He was then allowed to return to Mikawa Province. There, the Imagawa ordered him to fight against the Oda clan in a series of battles.<ref>{{Cite book |last=Bottomley |first=Ian |url=https://www.worldcat.org/oclc/63666433 |title=Shogun: the life of Lord Tokugawa Ieyasu |date=2005 |publisher=Royal Armouries |others=Royal Armouries Museum |isbn=0-948092-58-0 |location=Leeds, UK |oclc=63666433}}</ref>

Motoyasu fought his first battle in 1558 at the [[siege of Terabe]]. The lord of Terabe, [[Suzuki Shigeteru]] (or {{ill|Suzuki Shigetatsu|jp|鈴木重辰 (日向守)|vertical-align=sup}}), betrayed the Imagawa by defecting to Oda Nobunaga. This was nominally within Matsudaira territory, so Imagawa Yoshimoto entrusted the campaign to Motoyasu and his retainers from Okazaki. Motoyasu led the attack in person, but after taking the outer defences, he burned the main castle and withdrew. As anticipated, the Oda forces attacked his rear lines, but Motoyasu was prepared and drove off the Oda army.<ref name="Turnbull-I2">{{Cite book |last=Turnbull |first=Stephen |title=Tokugawa Ieyasu |publisher=Osprey Publishing |year=2012 |isbn=9781849085748 |page=10}}</ref>

He then succeeded in delivering supplies during the siege of [[Ōtaka Castle|Odaka Castle]] a year later. Odaka was one of five disputed frontier forts under attack by the Oda clan, and the only one that still remained under Imagawa control. Motoyasu launched diversionary attacks against the two neighboring forts and, when the garrisons of the other forts came to assist, Motoyasu's supply column was able to reach Odaka.{{sfn|Turnbull |1998 |p=215}}

By 1559, the leadership of the Oda clan had passed to Oda Nobunaga. In 1560, Imagawa Yoshimoto, leading a large army of 25,000 men, invaded Oda territory. Motoyasu was assigned a separate mission to capture the stronghold of Marune in the [[Siege of Marune]] operation. As a result, he and his men were not present at the [[Battle of Okehazama]] where Yoshimoto was killed in a surprise assault by Nobunaga,<ref name=Turnbull/>{{rp|37}} In the end, Motoyasu managed to capture Marune castle.{{sfn|Honda |2010|p=56}} 

Later, in response to the news of Yoshimoto's death, Motoyasu sent lookouts to check the state of the battle and then retreated from Odaka Castle at midnight. After leaving Odaka Castle, Motoyasu's forces headed for Okazaki with Asai Michitada as their guide. On the way, they were stopped by the Mizuno clan's forces at Chiryu, but because Asai Michitada was with them, they were not attacked. Having escaped from danger, Motoyasu entered Daijuji Temple outside Okazaki Castle the following day.<ref name="Hamada Kōichirō After Okehazama">{{cite web |author1=Yasutsune Owada (小和田泰経) |author2=Rekishijin Editorial Department |title=実は徳川家康は、桶狭間の戦いで今川方として獅子奮迅の活躍をしていた！|trans-title=In fact, Tokugawa Ieyasu fought bravely on the Imagawa side in the Battle of Okehazama! |url=https://www.rekishijin.com/26834 |website=Rekishijin |publisher=ABC ARC, inc. |access-date=24 June 2024 |language=Ja |date=2023 |quote=From "The Truth About Tokugawa Ieyasu" in the February 2023 issue of Rekishijin article}}</ref>

With Imagawa Yoshimoto dead, and the Imagawa clan in a state of confusion, Motoyasu used the opportunity to assert his independence and marched his men back into the abandoned [[Okazaki Castle]] and reclaimed his ancestral seat.<ref name="Turnbull-I2"/> Motoyasu then decided to ally with Oda Nobunaga.<ref name=sam>{{Cite book|last =Turnbull |first= Stephen R. |title= The Samurai: A Military History |publisher=MacMillan Publishing Co. |place=New York |year =1977|page= 144}}</ref> Motoyasu's wife, [[Lady Tsukiyama]], and infant son, Matsudaira Nobuyasu, were held hostage in [[Sunpu Castle|Sunpu]] by [[Imagawa Ujizane]], Yoshimoto's heir, so the deal was secret.<ref>{{Cite book |last=Bottomley |first=Ian |url=https://www.worldcat.org/oclc/63666433 |title=Shogun : the life of Lord Tokugawa Ieyasu |date=2005 |publisher=Royal Armouries |others=Royal Armouries Museum |isbn=0-948092-58-0 |location=Leeds, UK |pages=12 |oclc=63666433}}</ref>

In 1561, Motoyasu openly ended his allegiance to the Imagawa clan and captured [[Siege of Kaminogō Castle|Kaminogō]] castle. Kaminogō was held by Udono Nagamochi. Resorting to stealth, Motoyasu forces under [[Hattori Hanzō]] attacked under cover of darkness, setting fire to the castle and capturing two of Udono's sons. He then used them as hostages to exchange for his wife and son.{{sfn|Turnbull |1998 |p=216}}