The Pitcher

Pitch of World Destruction
A being born from the suffering of humanity, who wishes to return them to nonexistence.

The White wish to bring every universe to nothingness, although he is rumored to have been beaten by a yellow bear once...

TFR/Season 6
The White are the enemy that Heavy Machinery's erratic actions through the season were fighting, denying their chances to get close to the Messiah and ultimately forcing a stalemate that drove them away, saving the universe.

They also might've originally appeared to Kadoya Tsukasa in his original timeline and fought him after he had tried to use Delta's Alien Fax Machine and failed. However, what happened after that is unknown, they may have won and "purified" that universe, or they might have won and denied them.

Trivia

 * The White were supposed to appear in Season 6, but were discarded due to being too "high stakes".