Kagamine Len Prefix Title Token

"Kagamine Len's Special Note" Description:

 A note from Kagamine Len. If you complete a certain dungeon during the event period, you can earn a Prefix Title. Here's the hint for the place you must go to:
 A song for a sweet yellow rose.
 You need this note when you use the Prefix Title Coupon, so keep it safe.

Not sure but I ran a couple runs and my friends also ran some on their own. They got the token also. Dropped from Rabbie Adv. (From the clue we thought Yellow Succubus). I ran it 3 times and only the first run dropped a token. The second and third runs, no one in the party of 6 got tokens. So I'm not sure if this is a daily thing or not.

Ehh...how did you get the description? I thought the kagamine titles are for later(?)