Saiki/Story

Past
Saiki is the leader of Those from the Past, serving as the mysterious aforementioned "master" of said group from the "Tales of Ash" story arc's earlier installments. A being that has been described as the Western emissary of Gaia, he desires to gather life energy throughout the tournament to reawake Gaia's will and use the entity for his own means. To do so, he requires a particular ceremony to open a direct doorway to it.

The King of Fighters XIII
Saiki requests Botan to mind control Rose Bernstein to host The King of Fighters XIII in order to set up their master plans. Due to Magaki's death and Shion's sudden disappearance, they only have one shot in succeeding.

Saiki and the remining members of Those from the Past makes their move at the end of the tournament finals, freezing time and appearing before the winning team. Saiki tells them to get to their places, planning to finish off the fighters. Mukai wants to avenge the defeat that he suffered in The King of Fighters 2003, but Saiki instead kills him, absorbing his power and transforming into a large, muscular form. A large gate with time-bending powers appears in the distance, and he sends his underlings to gather more energy for the gate.

After the fight, Saiki remarks that they are doing well, though not good enough to satisfy him. He then suddenly notices that, instead of opening, the Gate was closing. Before he can suspect his followers of betraying him in some manner, Ash Crimson uses this moment of weakness to rob Saiki of his spirit. But, contrary to Ash's plan, Saiki finds him to be a suitable new host, manipulating the youth's body as his own and desiring to complete the job by fighting the winning team once again. He is defeated, however, and as Ash manages to retake control over his body after the battle, Saiki orders him to cross the gate so they can retry again. Ash refuses to restart time with Saiki, resulting in a time paradox and both being erased from existence.

In his non-canon ending (Bad Ending in Story Mode and in the original Arcade release of KOF XIII), Saiki barely succeeds, but due to various errors, he must start over from scratch and rewind time. He also laments on not being able to depend on Ash.

The King of Fighters XIV
Verse's defeat during the events of The King of Fighters XIV had released numerous souls and has caused many who have perished throughout the series to be brought back to life. Because Ash was revived regardless of his existence being a paradox, it is currently unknown if Saiki was revived with him.