The quest is unlocked after completing The Great Plateau scenario.
"Master Kohga is going to prove his toughness by taking on a test of willpower: fasting. Of course, he'll have to eat a big meal beforehand. The meatier, the better!"
"Master Kohga made it though his fast without a single slip-up! To celebrate, he treated himself to a sumptuous post-fast feast!"
- Master Kohga: Bonus Combo