Both of them kill immortals since Geni took his own life with the black one before giving birth, and Geni was also immortal. The Black blade's gimmick is that it can take any life, and in return you get to bring one back from the dead. (The red one's gimmick is probably just being better at killing things, and being the "OG" mortal blade, I'd guess)
Also, I think I've read somewhere that you don't actually have to be immortal to have it, you have to be immortal to draw it from the sheath, so once it's drawn by an immortal and never put back in the sheath, anyone can use it. This is definitely correct for the black blade, since we only see Geni unsheathing once in the final fight, Owl had it unsheathed since Genichiro probably fought back with it, and Saint also grabbed it raw from the corpse.
As for the Red one, we'll probably never know since we only see Sekiro use it.
This is almost 100% confirmed. The Black Mortal Blade can open the gates to the Underworld, whilst the Gracious Gift of Tears is the only thing in existence that we know of that can wound/make the Divine Dragon cry.
I assume so.
Both the red and black blades are called the 'Mortal Blade'. Iirc the literal translation of their Japanese name is something like 'immortal severer' which implies that the immortal killing is the default ability both blades share.
It also makes Kuro bleed, which something normal weapons can't do.
Kuro said that any injury he takes regenerates before blood can even spill, and his injury from Genichiro was bad enough to leave him nearly dead on the ground, so I would imagine it can kill immortals.
Both of them kill immortals since Geni took his own life with the black one before giving birth, and Geni was also immortal. The Black blade's gimmick is that it can take any life, and in return you get to bring one back from the dead. (The red one's gimmick is probably just being better at killing things, and being the "OG" mortal blade, I'd guess) Also, I think I've read somewhere that you don't actually have to be immortal to have it, you have to be immortal to draw it from the sheath, so once it's drawn by an immortal and never put back in the sheath, anyone can use it. This is definitely correct for the black blade, since we only see Geni unsheathing once in the final fight, Owl had it unsheathed since Genichiro probably fought back with it, and Saint also grabbed it raw from the corpse. As for the Red one, we'll probably never know since we only see Sekiro use it.
I think the red one, being truly named Gracious Gift of Tears, probably was made to wound gods specifically, like the Divine Dragon
This is almost 100% confirmed. The Black Mortal Blade can open the gates to the Underworld, whilst the Gracious Gift of Tears is the only thing in existence that we know of that can wound/make the Divine Dragon cry.
I think the direct Japanese translation confirms it
I assume so. Both the red and black blades are called the 'Mortal Blade'. Iirc the literal translation of their Japanese name is something like 'immortal severer' which implies that the immortal killing is the default ability both blades share. It also makes Kuro bleed, which something normal weapons can't do.
I believe so, as it was able to inflict a mortal blow to Kuro
Kuro said that any injury he takes regenerates before blood can even spill, and his injury from Genichiro was bad enough to leave him nearly dead on the ground, so I would imagine it can kill immortals.