Masou Kishin Cybuster

both have similar concept of a giant living mecha that is also an ancient god. both dance around such topics as environmental issues. 

both are mecha series about a giant living machine that came to earth from elsewhere. both have sibling dynamic. in both one of the parties' goals is revenge. 

both are set in japan after a massive catastrophe. in both there's a giant living mecha that is something akin to a deity. the plot revolves around the conflict between humans of earth and those from "the other side". 

More Cybuster goodness but in a different context