The Ninja World Hero Festival is an event added in version 2.08, alongside VR Master Haku.
The event is a week long, having players use their currently selected Master at the Ninjutsu Library to play in Base Battles or Combat Battles. During this time, the game will calculate the popularity of each character as well as your rank with them. If a player comes in the top 10 with their master will get a commemorative Honorary Title. You can get multiple Honorary Titles at once if you're in the top 10 of multiple Heroes.
The lobby is in nighttime and has stands during this game mode and Ninja World Face-Off.

NWHF logo

Hero's popularity and player's rank