These characters become available if you do the following actions during the game.

1) Stage 14A - Part 1:
Do NOT use Kira to defeat Shinn.

2) Stage 14A - Part 2:
Do NOT defeat Shinn at all.

3) Stage 15A:
Do NOT take out Shinn, Rey and Talia.

When you have accomplished the above Rey and Steller will then join in stage 30 in the Fafner route when Minerva appears to guide you.

Make Athrun attack and then convince Heine Westenfluss on stage 19-2.

When you have the following Game Boy Advance games in the cartridge slot the corresponding bonus will become an available option. The value of the bonus is in brackets),

EG Armor (45,000) - Super Robot Taisen A:
This part gives HP Regen (L) but does not stack.

Time Flow Engine (50,000) - Super Robot Taisen R:
This part gives EN Regen (L) but does not stack.

Res Arcana (55,000) - Super Robot Taisen D:
This part gives Double Image, Beam Coat (L), and HP Regen (S).

Orgone Cloud (70,000) - Super Robot Taisen J:
This part gives Double Image, Barrier (L), Ignore Terrain, and EN Regen (S).

Tesla Drive: Super Robot Taisen (60,000) - Original Generation:
This part gives Movement +2, Mobility +20, and Air Terrains S for both unit and weapons.

Z.O Armor: Super Robot Taisen (65,000) - Original Generation 2:
This part gives HP +2,000, Armor +300, and EN +150.

Prana Converter (100,000) - Super Robot Taisen D2. This part gives Attack +500, Range +1, Critical Rate +30, & Hit Rate +20.

When you reach Stage 25 select the Darius World route (B, 2nd option) and in stage 27B have Re Mii, Kotona and Souta fight Felme. At the end of stage 27B, Kotona and Re Mii's total kill count must be more than 150.

Allow Van to defeat the axe character in Stage 8 and in Stage 26A allow him to defeat Carossa. Then in Stage 27 have Vann's kill count reach the required level. When you reach Stage 31 part 1 defeat Woo and Fasalina first before defeating Michael. Michael and Fasalina will join after Stage 31 part 1

If you don't let Lou fight with any of the mimic monsters in Stage 15B part 2 you will get it after you complete Stage 30C part 2 (Godanner route).

This feature becomes an available option when you complete the game once and save. When you then load that saved game you will have retained half your money, your chosen favorite series and you will also be able to select a new senshin set for the originals.