Well, after reading the chapter, I inferred:
Imu is Lili herself. There are 19 swords, and the 19 kings/queens sworn not to sit at the Empty Throne.
Guess the only one who didn't sworn it? Lili! She mysteriously disappeared, didn't go back to Alabasta. Somehow she has been there for 800 years.
And, another IMPORTANT point: the Nefertari family is Nefertari D.
Ps: it's delicious to see Charlos get rekt
That's it