Koukyoushihen Eureka Seven, Kishin Taisen Gigantic Formula Recommendations
Kishin Taisen Gigantic Formula and Eureka Seven have a similar feeling to me. An average boy, a mysterious girl, and lot of secrets revolving around strange mecha.
Renton and Shingo are very similar in terms of drawing and personality. Both have messy brown hair and green eyes; both influence the other members of the organization. The mechas are both shrouded in mystery. Both leads fall in love with a mysterious girl.
Because they have simular sitiutation of "boy meets girl". Renton and Shingo have almost exactly same expression when they first met Eureka and Mana. Eureka and Mana chose Renton and Shingo to be their "partner". But the thing is different is that, Eureka seven have kind of less fighting and more love-y and Eureka and renton do even kiss in the end.