Naming
Shougeki has kanji, so that would mean "shocking". Gouraigan isn't a word.
Shou probably means flight.
Geki probably means violent, attack, or theater.
Gou probably means strength.
Rai probably means thunder.
Gan probably means stubborn or boulder.
Another thing to note is that all the given names for the characters are written in katakana.
Shôma Yamamoto is familiar with both the main director and writer's works, since he's a regular on Garo which is directed and written by Keita Amemiya, and played two characters on Kamen Rider Kiva (2008) such as Kamen Rider Saga (written by Toshiki Inoue)