The Matsui clan had a close relationship with Musashi MIYAMOTO, and there remains Musashi's letter to Okinaga ("the Letter to Nagaoka Sado-no-kami") which was written immediate before Musashi began to serve the Hosokawa clan.
松井家は、宮本武蔵が細川家に仕官する直前に興長に宛てた書状（長岡佐渡守宛書状）が残るなど武蔵と親交が深かった。