"A letter found in the dreamworld. You cannot decipher it."
The Encoded Letter (referred to as Decoded Letter upon deciphering it) is a key item found in Eric(a)'s Memories, in the room with Shelly. Eric(a) cannot read it on their own, but giving it to Wendy provides a translation, which reads as follows:
Dear revered mistress,
I have successfully finished the mission you have tasked me with, I am now at our secret location.
There have been no major problems, the magic you have bestowed me with works perfectly.Though I know I initially disagreed, I have come to realize what a boon being your student is.
In three days' time, I shall return, bringing you the spoils of the mission.
With honour and sincerity, your student.
- YoMi~
As of yet, the identity of "YoMi" is unknown.