He is voiced by Sōnosuke Nagashiro.
Extremely confident in his own strengths and abilities, Saiki believes himself to be a supreme entity of power. He talks in the same flamboyant manner as Ash, openly stating whatever lack of interest he feels. Saiki is rather malevolent and doesn't feel the slightest speck of remorse for the carnage he causes. He is very arrogant, and he takes pride in his "ascendant" status as an ancient entity and as such, has a "God complex" that is the primary source of his arrogant behavior, further reflected even in his fighting style. He often talks down on the fighters that face him, quipping sarcastic and rude dialogue towards his opponent (a trait that his modern descendant seems to have inherited) and often pointing out that he/she is a human, something Saiki considers as "worse than trash".
- Translocation - Saiki can translocate himself from one place to another.
- Dark Flames - Saiki can control dark flames, somewhat similar to the ones Evil Ash controls.
- Absorb powers - Saiki has the ability to absorb the powers from other people to increase his strength.
- Possession - Saiki has the ability to merge with and possess other individuals.
- Time Manipulation - Saiki is able to defy the flow of time at will, thus explaining the sudden appearance of Those From the Past.
- Shape/Size Shift - Saiki has the ability to transform from his "normal" state into a larger, more muscular form.
- Dark Energy Master - Saiki has the ability to control a special dark energy. He has displayed this ability only after absorbing Mukai's power (see Absorb Powers above), so it is unknown if this ability is inherent of him, or is absorption-dependant.
- Dark Energy Attacks - He can infuse his basic attacks (punches, kicks...) with dark energy for increased damage.
- Dark Energy Projectile - He can create waves of dark energy to attack distant enemies.
- Dark Paralysis - His projectiles can cover and paralyze opponents with darkness, leaving them open to Saiki's attacks.
As a boss, he focuses on immobilizing the opponent using his Tokoyami no Fune (Ship of Everlasting Darkness) at both long and close range, followed by either the Kyoryuu no Ori (Distant Dragon's Sediment) - a 4 hit grapple - or his Super Special Move Kasumi (Divine Flock), dealing a considerable amount of damage.
As a playable character, Saiki uses an acrobatic fighting style using kicks, projectiles and teleporting. Most of his Super Special Moves are stronger versions of the Special Moves of his Awakened Form. Tokoyami no Fune is now a very powerful projectile move similar to Ash Crimson Super Special Move Thermidor; his Kyoryuu no Ori drains the opponent life and Kasumi (as his Neo Max Super Special Move where he briefly turns into his boss form) turns into a screen filler.
- Toki Wo Suberu Mono (The One Who Rules Time) - The King of Fighters XIII (normal form theme)
- Fate - The King of Fighters XIII (Awakened Saiki, boss form theme)
- Fate ~Arranged~: The King of Fighters XIII (when the music is set to "Type B", console version only)
- The King of Fighters XIII - Sub-Boss (DLC character in his Human Form, as EX Saiki)
- All of his moves also have their particles in the Japanese script written with katakana instead of hiragana, and are also written as puns/plays on similar pre-existing terms (but some with different kanji).
- Saiki and Rugal Bernstein are the only bosses of the series (sub or final) with two or more versions of their persona. The personas of both characters can be coexisiting in the same game (KOF XIII and KOF '98 [and its remake], respectively). However, unlike Rugal, Saiki's versions can coexist canonically.