Fan Translation:
He who wears this mask shall become a demon.
Which is why, it is to be done only when push truly comes to the shove―――.
Of course, I had thought that it was simply a joke.
This mask is simply a mask. It does not mean that wearing it will actually turn one into a demon.
Yes. However.
In the case that this mask is worn, and the wearer actually turns into a demon.
In the case that the wearer change into a rakshasa, capable of completely obliterating our enemies.
In the case that it can rescue us of the Fuuma clan from our predicament.
I will, surely―――.
And now, after wearing the demon mask, I understand.
I see. I certainly turned into one.
Simply by covering one's face with it makes it possible to commits all kinds of demonic acts and vices.
Already, I am unable to remove this demon mask.
As I embrace wickedness, the rest of the Fuuma fall down together with me.
Forgive me, father.
For I had already been reduced to a mere demon.
Trivia
Special thanks to castor212 of Beasts Lair for his translation.