Super Robot Taisen J [GBA]
Defeat Takuma as Sousuke on stage 24. Defeat Zaied as Sousuke on stage 29. Defeat Gauron as Sousuke on stage 30. You should get Bonta-Kun on stage 34.
Unlock Fourth Original Mecha:
Complete the game with the Bellezelute, Coustwell and Granteed.
Unlock Gai Daigouji:
Take the Nadesico Route on stage 21. Gai Daigouji will join you during stage 44.
Do not use Zeorymer you are forced to. Go with the Nadesico on stage 11 and allow Zeorymer destroy Lanster of Wind. On stage 21, go with the Archangel and allow Zeorymer to destroy Briest Of Fire and Gallowin Of Water. On stage 29, allow Zeorymer destroy Rose C'est la Vie of Moon. On stage 32, allow Zeorymer destroy Dinoderos of Earth, Burrstone of Mountain, and Omzack of Lightning. Great Zeorymer will appear afterwards. Destroy it as Zeorymer. Great Zeorymer will appear on stage 36.
Go with the Archangel on stages 11 and 37.
Do not destroy the Nobel Gundam on stage 38. Convince Allenby with Rain on stage 41. Then, destroy the Nobel Gundam.
Have Tekkaman Blade defeat Tekkaman Evil on stage 34 and Tekkaman Axe on stage 36.
Take the Nadesico Route on stage 32.