Quest #108 Top-Flight Knight Fight - Mirage Mahal (Gleeba)
Quest Requirements: Use H-pathy on someone with 1 HP five times during battle
Quest Pre-Requirements: Level 40+ Paladin and Side Quest #107 Complete
Reward: Paladin's Primer and Solar Flair
This quest is given to you by Brunhild, the Paladin on the roof of the Mirage Mahal in Gleeba that gave you the Paladin Class Unlock Quest and Side Quest #107. In order to accept this quest you'll need to have completed Side Quest #107 and have someone in your party who is a Level 40+ Paladin.
For this quest I recommend you go to a dungeon that has floors that damage you when you step on them. Keep running back and forth over them until a few characters have 1 HP then go into battle and use H-Pathy on that character. You can only do this a single time per battle so it'll take 5 battles in total.