Rasetsu is the Black Spider Clan ninja who mutates into a large, half-human and half-spider form in which he assaults Ryu Hayabusa with. First appearing as the boss battle of Chapter 1, another Rasetsu shows up in Chapter 2 with a group of minions aiding him. After fighting well into the Amazon in Chapter 10, Rasetsu becomes an average enemy and it becomes possible to fight at several at once, each as powerful as the first time he is fought. Also appearing in Ninja Gaiden: DS, his/their moves do not differ between the games.
- Capable of launching twin blades of wind.
- Rushes forward using all limbs and performs a grab.
- Has a standard three hit combo where he flips forward and attacks.
- Has a four-hit combo attack ending in a kick.
- Has one jumping attack where he leaps high and comes crashing down on his opponent.
- Has a single, high-power attack where he jumps back and flips forward to crush Ryu with all arms.
- Capable of relatively high speed.
- Grabs do a great deal of damage, especially on higher difficulties.
- When encountered in Chapter 2, on higher difficulties, or as a regular enemy, Rasetsu is often aided by other enemies, be it a fellow spider or enemy ninja.
- Some moves, such as the Flying Swallow, have limited effect on Rasetsu as most of the time the move will simply be blocked.
- Not so much a danger, but Rasetsu will perform a taunt where he rears back with all of his arms outstretched and let out a scream.
- Every time Rasetsu attacks he tends to leave himself open for a period of time long enough to engage a decent combo.
- Before tossing his blades of wind at you, there is more than enough time and warning thanks to the sound he makes with which you can prepare to avoid his attacks.
- If facing Rasetsu with multiple enemies at helping him, his own attacks are more than capable of taking them down, but they generally respawn if killed by Rasetsu.
- Quick combos, Ultimate Techniques, and Ninpo work wonders on Rasetsu.
- Once weakened, you can perform an Obliteration Technique on Rasetsu.