To begin the 28. An Oracle’s Ailment side quest in Trinity Trigger, speak with the Queasy Oracle at Lavaxia. For this quest, you’ll need to find an Antidote Stone in the Lavaxia Trail: South. This item can be found near a mimic chest in the northern part of the blue area as shown in the map below.
Once you retrieve the item, return to the Queasy Oracle at Lavaxia to complete the quest. As a reward, you’ll receive a Status Effect Removal and Panacea x2.