Ishida is a Clan in Nioh.
Based around Mount Sawa in Omi province (Shiga prefecture today), the Ishida clan were retainers to the Toyotomi administration. Their best-known leader was Ishida Mitsunari.
Mitsunari's respectable family background saw him serve Toyotomi Hideyoshi from a young age, proving himself as a military administrator. After Hideyoshi seized control of the country, Mitsunari was tapped for a role as an official. His skills as a negotiator made him one of Hideyoshi's most trusted advisors, but his poor relations with retainers like Kato Kiyomasa and Fukushima Masanori, whose skills were superior on the battlefield, ultimately contributed to the fracturing of the coalition Hideyoshi had built.
The Ishida clan's flag reads, "Fortune smiles when one serves all, and all serve one", meaning that when the people join behind a righteous leader and the leader works for the people, then peace and prosperity will follow. It is said to have been chosen by Mitsunari himself.