To go back
Izuku had failed, he hadn't been able to save them.
There was the attack on USJ where some of his class died.
There was the training camp where he failed to save kota and Kacchan.
There was All Mights fight with All for one.
All Might had died and Izuku couldn't help
Heroes got routed quickly without the symbol of peace.
His friends had fought hard but fell.
Heroes were wiped out.
All For One gained control of Japan.
With Japan under the control of a villain, countries from all around the world sent forces to try and stop him to no avail.
Those countries soon fell too without their own top heroes.
Izuku had tried his best, but he failed everyone.
But now that he found himself back in the past?
He could change what happened.
He had to make sure that All Might didn't give him One For All, He had to make sure he wasn't to be the 9th holder.