Blake might have no single idea about the main element that the greenish demon used in its spells, but when it comes to darkness element runes, Blake could be said to be more than just proficient in them.
He had memorized and learned the use of so many darkness elemental runes that he even had some that were still sitting at the back of his mind and haven't been used yet in any of his spells.
And the rune that he currently saw in the greenish demon's spell was one of those runes that he knew but didn't use in any of his spells.
Digging into his memory, Blake instantly recalled the rune's use.
"It's the rune to emphasize the darkness element in spells," Blake muttered out loud as he double-checked whether the runes that he saw were the same as the ones in his memory.
After taking a good look at the rune for a solid 5 seconds, Blake was then sure that it was indeed the rune that he was thinking about.