Flash Blade is a minor character from the NES Strider. He's fought twice as a mid-boss in the Red Dragon stage. Out of the 4 mid-bosses exclusives of the game, he's the only one with no lines or in-game dialogue.
Not much is known about Flash Blade. His costume is similar to Ryuzaki's, which seems to indicate he's a Strider. He's a follower of Matic and member of his private unit. His weapon of choice are two long blades, which are apparently attached to his arms. He uses them to block by crossing them in front of him and attacks by spinning rapidly, turning himself into a flying top weapon which bounces off the walls and ceiling, making avoiding him difficult.
Flash Blade remains in the Red Dragon station as part of Matic's private unit, keeping under protection the ZAIN Project's Main Tree, Yggdrasil. During Hiryu's infiltration of the station, he's the first of Matic's men who attacks him, right after his boss claims Hiryu has no chances of coming out victorious. Hiryu and Flash Blade fight and he's defeated.
Once Hiryu has unlocked the door to Yggdrasil's chambers, he has to face off against him once again, holding the last line of defense before Matic himself. Much like the first time, he's defeated again.
In battle, Flash Blade follows a specific pattern: he starts the battle by running at Hiryu with both blades crossed in front of him, and he becomes vulnerable only after jumping. Once hit in mid-air, he turns into a human top and starts spinning from bottom to top of the screen twice before restarting his pattern again.
His flying top attack appears difficult to avoid, but it follows a predictable path: Once hit, he flies towards Hiryu's side of the room following a diagonal trajectory and bouncing around when hitting a wall or ceiling, and ends with him spinning at ground-level in a straight line. Once his pattern is understood, it can be easily avoided by jumping and sliding at the right times.