By having the any of the following GBA Games in Slot-2 of the NDS with Ryuusei no Rockman:

Battle Network Rockman EXE (Megaman Battle Network)
Battle Network Rockman EXE2 (Megaman Battle Network 2)
Battle Network Rockman EXE3 (Megaman Battle Network 3 White)
Battle Network Rockman EXE3 BLACK (Megaman Battle Network 3 Blue
Rockman EXE Battle Chip GP (Megaman Battle Chip Challenge)
Rockman EXE4 Tournament Red Sun (Megaman Battle Network 4 Red Sun)
Rockman EXE4 Tournament Blue Moon (Megaman Battle Network 4 Blue Moon)
Rockman EXE4.5 Real Operation
Rockman EXE5 Team of Blues (Megaman Battle Network 5 Team Blues)
Rockman EXE5 Team of Colonel (Megaman Battle Network 5 Team Colonel)
Rockman EXE6 Cyber Beast Greiga (Megaman Battle Network 6 Cybeast Gregar)
Rockman EXE6 Cyber Beast Falzer (Megaman Battle Network 6 Cybeast Falzar)

And either still in or taken out after a saved game. A New Cutscene will commence in the Dog House next to Gonta's House. After the cutscene is finished, go to the statue near the stairs to fight enemy in the middle of the map. Finally, after defeating the enemy, go back to the Dog House.

A Cutscene with Rockman EXE will occur out of the Data in the Dog House. You'll give him the Data picked off the enemy you defeated for a War Rock Item, "EXE Blaster". Which stats are AT1 | RA5 | CH1.

Slot-2 is also Region Locked for bonuses. Meaning Slot-1's Game must be in Japanese if you want to use Japanese Slot-2 Carts and vice-versa.