Darkness

Darkness is Yami's innate ability of transformation into the disastrous form that even overwhelms Nemesis. Initially, Yami cannot control the power of Darkness as the ability activates when Yami sincerely accepts the tranquility of her mind. And the strength of Darkness gets emphasized when Yami suffers an excessive stress to her mind.

It is apparently set as a trap against the peace of the universe as the Galactic War seems going ceasefire.

However, the ability Darkness finally gains glitch because of Yami's love toward Rito as her friends help Yami inoculate with the glitch making her return to normal. And she also obtains containment to activate the ability at will.