Shiki in the Manga

Shiki was one of the members of the Tao clan whose ancestors survived the war against Chronos 25 years ago (He confesses to Train in their battle that if he was old enough, he would have participated in the war, though). As a Master-Level Taoshi, Shiki manipulates his Chi (His - even though his gender can't be determined in the first volumes due to his garb, later on the story he reveals his identity). Shiki's main form of offense is through the use of insect summoning, and as such, his Tao Power is called "Insect". However, besides his insects, he masters the usage of ink seals, using them for manipulating his Ki in various ways, ranging from creating a seal sword to creating an energy blast.

Shiki in the Anime

Shiki's backstory is not revealed in the anime. He also does not fight Train or show any kind of major role in the Apostles of The Stars, as he is part of the elite team summoned by Mason to put into motion the Eden project, although he is often seen using his insects to gather information for Creed. He fights Anubis.

Source: Wikipedia