My best guess... the elder must have poured enough power to "bring their friends back" for only a few seconds.
There is a chance, too, that it was their stored memories in some way, but considering how they reacted, chances are that he was able to "resurrect" them for just a moment.
Seeing how it activated only when Hajime was close to killing Blood, it may have been a conditional effect.
Hajime's skill is broken in a way, seems like the type of skill that is a big F.U. to debuff skills and DOT type, or you kill the holder in one go, or you are in for hurt... but the drawback is pretty clear, it doesn't seem to buff recovery, only attack power, so it he uses it without thinking, well... he had so many unseen scars for a reason.