During "The Flash: Rebirth," mysterious deaths began occurring on Earth-0. Large numbers of speedsters died bizarrely at night, leaving not even intact corpses behind—only piles of black ash.
After investigating, Barry finally discovered that the culprit was the Speed Force controlling him at night, transforming him into Black Flash.
There were too many speedsters, and even more of their Hypertime Variants running around everywhere. The Speed Force was overwhelmed, so it simply turned its strongest Flash, Barry, into the Speed Force Death—a cleanup tool to eliminate the excess trash.
After all, when Barry was asleep at night, his body was just lying in bed. It was not like he had anything better to do.
The Speed Force had helped Barry so many times and saved so many people. So this time, it thought that asking Barry to help it in return just once should not have been a problem, right?
Barry was stunned, then overcome with grief. After that, he decided to kill himself and give up his "share."
After all, he was the one using up the most Speed Force. He could kill himself in the Speed Force Plane, return his Speed Force to it, and trade his own death for the lives of the other speedsters.
But then a Batwoman emerged from the darkness. Leading the Justice League, she beat Barry, who had transformed into Black Flash, to the ground and refused to let him die. She even used tactics prepared long ago to drive off the will of the Speed Force itself, forcibly saving Barry.
Because Batman was the best detective on Earth, he had actually found out who was behind the serial murders long, long before Barry himself discovered the truth.
However, to make the other members of the Justice League realize that Barry had been