By having the any of the following GBA Games in Slot-2 of the NDS with Ryuusei no Rockman 2:
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 Mail message with Goyouda Heiji will be obtained. He'll want you to get Data found in the different Radio Networks.
1/XX: Kodama Town ~ Post Box Radio Network (Already Unlocked)
3/XX: TK Tower 1 ~ Old Binocular Radio Network (Inspect at OphiuchusQueen Scenario)
7/XX: Food Town ~ Forgotten Ice Statue Radio Network (Already Unlocked)
9/XX: Donbura Lake Area 1 ~ Sunken Ship Radio Network (After CondorGeograph Scenario)
11/XX: Nansca ~ Lower Wall Radio Network (After CondorGeograph Scenario)
The Data Items are Diary Entries of an Old Protanganist and also can be read in Items for each of them. Obtaining all of the Data Items gives you an Mail from the Old Protanganist with the "EXE Blaster" attached. 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.