Mercury

When we are introduced to the seven people who want to become Holy Men, we see that they are all aligned with a planet except for Mercury.

There is a clue as to who is represented by Mercury.

During the scene where they all head off on a boat, they all carry staves with planetary symbols. The naked woman with symbols (credited as the "written woman") is carrying a staff with the Mercury symbol on it.

It should be interesting to note that The Alchemist is carrying the Sun symbol.

It makes me wonder what "The Written Woman's" background is... She has healing powers, which is in line with Mercury. Maybe she has some educational capacity as well.