Diederich has long, golden hair and vibrant greenish-blue eyes, showing his resemblance to Risa. He is mostly seen wearing his knight uniform.
Diederich is the older brother of Risa and used to play Magnolia Online in his free time. He had a very complicated and toxic relationship with his sister while playing the game and emotionally and verbally abused her, but it seems he will be leaving her alone from season two onwards.
This might be because at the end of season one, he told Risa that he was quitting gaming. His character has made no appearance since then.