A 2005 Super Robot anime series by Satelight, created by Kawamori Shouji. An alternate retelling was released as an OVA in 2007.
The series was followed by Aquarion EVOL, a 2012 sequel.
In Sousei no Aquarion, three manned giant robots transform into a bigger one called "Aquarion", during which each of the pilots of the titular mecha have an orgasm each time they "merge", which they then use to fight the mysterious Shadow Angels.
This tag implicates aquarion_(series) (learn more).