Arad Senki: Slap-up Party is the Japanese anime adaptation of Dungeon Fighter Online beat 'em up action RPG franchise, and the first incarnation of the DFO media.
It is loosely based on material from the official webcomic, The Vagrants in Arad (aradeuui bangrangpati, Japanese: Arado No Hôrô Pâtî, lit. The Wandering Party of Arad), featuring several of the same characters.
Adapted from the MMORPG Arad Senki originally developed in South Korea under the name Dungeon & Fighter, where NHN Japan says is it the most popular action RPG.