It's Imu
Teach is just Obito /Aizen
Xebec is Madara/Aizen
Imu is Kaguya /Yhwach
Obito wasn't hyped as a rival to main character through the beginning of the series. Obito was defeated by Kakashi lmao.
Kaguya was a secret until the last battle, Oda already exposed Imu's secret much earlier.
Also Kaguya was defeated by both Naruto+Sasuke, not by Naruto.
Who is Luffy's Sasuke?
Debunked.
It is a possibility. If the ope ope operation was actually done in the OP world then there must be a way to undo it.
If something is taken it is taken, but if something is added on the other hand.. let's say Law removes an heart, if the yami user touches that then the ooe power in the person can be undone but the heart can not be teleported back, so the insides turn in a mess said people dies almost immediately, if an arm is cut by a df then BB of course can not make it come back, same as this.
But if a body gets a plus thanks to a df, be it make flames, turn into strings.... And probably become immortal too, then I think it could work. But it is just an hypothesis.
Definitely there is something to counter immortality but don't think it's BB fruit
Either it's Nika somehow or current user of ope ope no mi himself
Or the immortality is not from the ope ope, Oda had Iva remembering exactly that because that is what every reader would think, and instead it is related to some other factor and only a "D." can actually destroy it (and that is why Imu hates the D.).
It shouldn't be any different than having a DF power since its immortality comes directly from Ope DF and the Ope user sacrificing its life to accomplish it. Similar to how DF user needs to die before someone else taking the DF.
A different version of Brook's DF, if Teach uses darkness on Brook, Brook won't be able to reassemble his bones again. Or Marco can heal from even Haki attacks, but if Teach uses darkness on him he won't be healing while being hold by darkness.
Teach knew about Ope immortality, perhaps thats why Teach searched the darkness fruit, to counter someone who become immortal with Ope DF, not only counter Nika DF hax + other Hax DF abilities.