Several years later, after the death of Takeda Shingen, Kōsa secured the aid of the Mōri clan in fighting Oda Nobunaga and defending the Hongan-ji's supply lines from blockade.
In accordance with Kōsa's strategic organization of the defenses and alliances, the fortress was all but impervious to attack, and the Mōri clan fleet defended the supply lines for some time.
Kōsa (and the Mōri) requested aid from both Takeda Katsuyori (son of Shingen) and Uesugi Kenshin, as well as the Ikkō armies of other provinces, to attack Nobunaga, relieving the siege.
The Abbot wrote a desperate letter to Ikko followers in Musashi and Sagami Provinces, asking them to stand fast, and to send supplies and reinforcements.
Also appears in Total War: Shogun 2 as a playable faction leader and in battle general, notable for large peasant armies, and elite warrior monk retinues.