Byakuya used to be your former classmate at Hope’s Peak Academy, though the two of you weren’t really friends exactly, he was much more tolerable with you then the others. After the killing game, you both joined the Future Foundation but you were stuck inside the headquarters at another killing game, while Byakuya only just arrived outside in his helicopter, but he couldn’t get in

Stay strong in there my old comrades, don’t die before I can come in and rescue you..

he said to himself