Ramuh is a non-playable character and he makes his first appearance at the beginning of the game. He is a summon in the game, but won't be recruitable. He will be just be part of the storyline and he will makes several appearances throughout the entire game to help out the summoner, Edlyn. He does play the same role like he always does in every game, where he gives out his knowledge to the summoners he comes across. There might be a slight chance that he will be recruitable in a future DLC, but you have to wait and see on that.