"I need something delivered in a timely and discreet manner."
"Deliver this letter. There's no address, but perhaps you can figure out who the writer was referring to when he said "Someone in her position.""
Quest-Giver Dialogue 
"I know it's inappropriate to write love letters to someone in her position, but I can't help the way I feel. It may only inconvenience her, but...could you deliver this?"
Quest Completion Dialogue
"You actually did it? You delivered it to Lady Rhea?! That's so embarassing! How will I ever face her...Ugh. Well. Thanks, anyway."
Given to you by a male student near the entrance of the Cathedral.
- Crescent-Moon Tea x2
- Blowfly x2
- Landscape Painting x1
- 300 Renown
Subjective: The following part of this article is based upon the editor's personal experiences and opinions, and therefore may not be applicable for all readers.
Talk to the student near the entrance of the cathedral and accept the quest. Byleth will then receive the "Reverent Love Letter". Head to the Audience Chamber and give the letter to Rhea. Report to the requester to finish the quest.