On May 18th, Imagawa Yoshimoto made a stop at Kutsukake Castle. Kondo Kageharu was in charge of the castle at the time. This would be Yoshimoto's last stop before his violent death at the Battle of Okehazama.According to Owada Tetsuo's Okehazama no Tatakai, Kageharu served under Matsudaira Hirotada (p. 42). After Okehazama, the castle was attacked by Nobunaga and Kageharu was killed.
For his reward for the intelligence, Yanada Masatsuna was given money and Kutsukake Castle.
One of the reasons why Yoshimoto stopped at Kutsukake Castle was to rest his troops, gather some last minute information on the Oda, and plan out the rest of campaign. Your best bet to visit the castle ruins is to get off at Zengo Meitetsu station and take a taxi.
Tenka no tame!