—Command Spells.
Under normal circumstances, these were abilities—or rather, marks—that only Masters capable of commanding, summoning, and having Servants fight for them could possess.
Their essence was a crystallization of magical power, a symbol of a Master's identity, and also a consumable resource.
Normally, every Master possessed three Command Spells. Each time one was consumed, the Master could strengthen, heal, summon, or even force a Servant into obedience by issuing a command.
As long as it was within a Master's capabilities, they could use Command Spells to make Servants do things they normally could not, including but not limited to matters approaching the realm of magic such as Spatial Transfer, or even ordering them to kill themselves.
Fujimaru Ritsuka, the Master of Chaldea whom Riezel had once encountered in the Fairy Kingdom of Britain but had barely spoken with, possessed Command Spells engraved on the back of his hand.
Chaldea's summoning ritual had turned that not particularly capable mage into a Master and granted him a lightweight set of three Command Spells. Though these three Command Spells could not issue absolute commands or reproduce miracles, they could still be used as a source of magical power, allowing Chaldea's Masters to strengthen or heal Servants by consuming them. Thus, Command Spells were treasures every Master cherished.
And now, Riezel suddenly realized that his Holy Sword Rune seemed remarkably similar to Command Spells, both in appearance and effect.
"The Holy Sword Rune can convert Holy Sword Power, allowing it to be used in any aspect."
"It can be used on myself or others. It can even be used through the connection of a contract, on retainers or even on the contracts between retainers."
"If that's the case... it seems I can also consume Holy Sword Power to strengthen retainers by issuing commands.