Code Geass: Boukoku no Akito 4 - Nikushimi no Kioku kara

Both shows are about squadron of soldiers surviving the harsh world and involves young soldiers. Akito's relationship with Leila is similar to Mikazuki with Leila as a nod to Heero and Relena plus they are all based on their archetype. Not to mention that one of the characters in Gundam IBO has the same seiyuu and a similar mecha with a relationship with the other character who too has the same seiyuu.