"Kokoro no Seijaku, Tsurugi no Hayasa"
That means "the stillness of the mind and the swiftness of the sword".
Actually in the English original there is some subject who is omitted. So it is more like "his mind is still and his sword is swift". Maybe it is more like "heisei na kokoro, binshou na tsurugi" (平静な心、敏捷な剣)