At the Eris Festival, Megumin runs into a masked member of the Silver-Haired Thief Brigade and immediately decides to found her own band of thieves in imitation. Yunyun and a girl called Alice get pulled into the scheme, whether they like the idea or not. Set between volumes eight and nine of the main Konosuba story, this sequel manga follows Megumin's self-styled gang of vigilantes as their good intentions collide with her usual chaos.