KBrO4 + 7 KBr + 4 H2SO4 → 4 Br2 + 4 K2SO4 + 4 H2O
This is an oxidation-reduction (redox) reaction:
7 Br-I - 7 e- → 7 Br0 (oxidation)
BrVII + 7 e- → Br0 (reduction)
KBr is a reducing agent, KBrO4 is an oxidizing agent (synproportionation (comproportionation)).