So how many solutions to that riddle have we come up with so far?

- Shannon and Kanon are the same person, plus Erika is 17
- Erika is actually one of the other 17 on the island
- Both of the two above are true, leaving room for 17th Person X
- The number system used to count people starts at 0
- The number system used to count people is not decimal
- There were only 17 people on Rokkenjima-prime, even if Erika is a piece
- There were 17 people after the first twilight so there was room for more people
- Battler falls off the boat, and the rescued "Battler" is really Jessica, which is 17 people
- "Furniture" don't count as humans, so there is room for 3 extra people
- Battler doesn't exist and is only a "personality"

Any others I forgot?