This is inspired by something I've seen in another game I've played: Fire Emblem: 3 Houses (2019).
If a player manages to defeat the highest difficulty of the game (Maddening) without the benefits of NG+ (New Game+, Progress and benefits can be optionally carried over from a previously cleared save file) on any of the four available paths, the game's main menu changes (See attached screenshots) to reflect the player's achievement.
I think something of a similar caliber could be used to reflect a player's achievement of completing Dominating Difficulty in Underrail.