He doesn't even need any mana in order to use this feature, whereas when he's in the Storage Ring, every time he needs the Shadow Sword, he uses mana in order to summon the sword and requires some concentration for that.
Which makes him lose some focus in the fight. Just one mistake while fighting a demonic animal, demonic beast, or human was considered extremely dangerous, both for him and for the rest of his future allies.
Losing concentration during combat, even for the slightest moment, could lead to his death or the death of any of his colleagues, so he preferred to use this new ability that he discovered by chance when his sword fell on his shadow and absorbed it.
Imagine his surprise when this happened. As soon as he thought about the place where the sword had disappeared, the sword began to emerge from within his shadow in front of his eyes, and he looked at it in shock from there. He started using this method all the time.
