The katakana say "Soono" and Somno is just my liberal interpretation of that, but I went with the assumption that there's a pun on somniare (to dream), the same way Doremy's name resembles dormire (to sleep).
Updated
I come with a request for you, seeing as you're so skillful at wielding lucid dreams.
I am the "ruler of dreams", Somno Sweet.
Good evening.
This is my dream! No one else should be able to enter...!