Your search for "/ frederick x prussia" revealed the following:
Fire Emblem Awakening BL GAG Doujinshi - It's Candy Numbskulls! (Chrom x Gaius and Frederick)
$ 26.95Product details: Chrom x Gaius and FrederickIs Gaius eating swords, bear's fingers and raven's claws? Frederick spies some horrifying sights...