[Kioras]

Quick Theories, with spoilers.

Spoiler for Theory from untranslated novels.:

I understand from some of the spoilers that they are looking for someone to be the Dark Queen, to control the awakened Kamito, and any of the girls who are involved with him are elligible.

My theory is that from the group there will be 6 'true' or 'hidden' queens, one for him, and 5 others for each of the hidden/lost/sealed 'old' or 'true' elemental kings.

The first one may be Rinslet who may make a contract with Iseria Seaward from the ruins.
The second may be Claire who could be the Dark Queen.

There are his other 2 teammates Ellis and Fianna, who may qualify later, with an unknown spirit king. Then there is one from outside of the team that per spoilers has quite a bit of time with him and that is Leonora. I don't know who else may or may not have been with him enough to raise enough flags.

And some more speculation on future arcs.

Spoiler for Future Arcs Speculation:

I see the blade dance finishing up with a finale in the next 1-2 novels. That will finish the third main story arc.

After the blade dance is finished, I see the next major arc being a hunt for the missing/lost spirit kings, with each king taking a novel apiece. There may be background events happening at the same time however.

After the Hunt for the spirit kings, i see a final arc being an eliminate the current/fake kings, again taking about 1 novel for each one. This would also give more time for each of the main heroines to star in a novel.

Final Wild Mass Guess Theory in regards to the prior dark king. I don't have enough info/spoilers from book 10 to make it any more the mass guessing.

Spoiler for Dark King, WMG:

There could of been 2 dark kings in the past. The most recent one was terminated by the Est and her prior contractor, this one may be the one that is a shadow that is controlling 'snake'. Before that, their may of been the true dark king that fought in and lost the spirit war against the current fake kings. Unlike the fake kings, he was removed from history, without anyone taking his place.