Sayo

Sayo (小夜) is an original, unique, playable character (once the player reaches Level 3 Regards with her), and the true main antagonist in Warriors All-Stars. The supernatural being who shares her form calls itself Yomi (夜見).

Role in Game
She is Tamaki's and Shiki's mother and Setsuna's aunt. She is the only priestess blessed by the divine spring. When the spring dries up and her world begins to wither, Sayo informs her relatives that it is necessary to restore it and only Tamaki has the power to do it. Her words cause Shiki and Setsuna to distance themselves from the Holy Castle.

At the start of the game, she helps Tamaki summon the otherworldly heroes and introduce them to their world.

Development
Furusawa remarked that the original characters in Warriors All-Stars were originally designed to be human beings, but the team felt that their visuals "lost entirely" to characters from other IPs. They then tried to make the original characters appear to be "almighty", but this was declined for going too overboard just for the sake distinguishing them. Their current beastly appearances were originally suggested by one of the game's designers. It was accepted since anthropomorphism wasn't present in the other Warriors IPs that they had picked.

Personality
Calm and elegant, she is a perceptive woman who is loved by her people. In reality, she is very manipulative, crafty, egotistic, arrogant, hateful, resentful, deceptive and destructive, especially when the demon form Yomi has possessed her conscious mind.

The demon form Yomi is the result of the corrupted, twisted and tainted form of the original Goddess-Creator Yomi, who had once fought the darkness of her world alongside with her people long ago. Once she realized that she is about to be corrupted by the exactly same darkness which she was trying to fight off, she asked the first king to seal her away into the holy spring with the three Sacred Weapons, causing her good and evil side to separate.

The first king, who'd reluctantly sealed away Yomi into the spring, then had left his message with the Monument of Dawn very secretly and personally, begging his descendants to purify, rather than to seal, Yomi using the Sacred Weapons.

Sayo

 * Normal Attack: Sayo sparks a single ball of energy two times shooting sparks from them, then two orbs above one another, then two orbs in between, then shoots sparks in a fan formation, then makes an energetic explosion.
 * Charge 3: Sayo sets a symbol on the ground and makes it burst out spikes.
 * Charge 4: Sayo makes three symbols and bursts lightning.

Yomi

 * Normal Attack: Yomi slowly throws a ball of magic, then three more, then throws two more magic balls, then three all around.
 * Charge 1: Yomi sends out a large shockwave pushing all the enemies away.