Giniro no Olynsis: Tokito

These to follow almost exactly the same story line, guy meets strange, other-worldly girl, guy becomes pilot of massive humanoid robot that saves the world, end of story 

The Character's Are look alike and They Have The Same Character Designer. Both Have Mecha/Romance, And In Gin-iro no Olynssis the Earth is Being Invaded by a Different kind of Creature's, in Gundam Seed The Earth is Being Attacked by Coordinators. 

The setting is almost exactly the same, and the plots are somewhat similar. The characters have some major differences, though. Gundam's characters were more likable, and the characters were more believable.  

AI, Mecha, plotline and setting are very similar. you could almost call Gin iro no Olynsis a predecessor to Gargantia 

both have a mysterious female main character, and both are about creatures coming from the moon, the two fall in love and people are trying to seperate them.  

both have the same problems/story when it comes to the love/ relationship portion of the show. the main character (female) are both mysterious and powerful and fall in love with an average guy. both the males have childhood friends that are in love with them.  

Boy meets supernatural girl for pilonting a mecha 

Both Anime Has the Same Type Of Story But Different Ending, In Gin-Iro No Olynsis The Earth is Being Attacked by Gardeners(Creatures From the Moon) That Trying to Erase the Remaining Human Kind and in Dragonaut the Earth is Being Attacked by the Thanatos(Giant Dragon) That Roam Around the Universe Destroying planets that contains its Dragon Egg's. In Gin-Iro No Olynsis The Girl Main Character can Transform into a Robot and Can be Piloted Only by the Chosen One. In Dragonaut The Girl Can also Transform into a Dragon and Can be also Piloted by there Resonance.  

You put Zoids (any Zoids series) and Gundam Seed together, and you get Gin-iro no Olynsis.