>>2021665
Adult + master class quests: https://dbocom.com/forum/showthread.php?p=79928
Tl;dr: Break a box like picrel, loot the red talisman thingy and follow the quest chain until you're allowed into Korin's Tower.
Permanent flight: https://forum.dboglobal.to/index.php?thread/10189-english-flight-quest-chain/