Andersen is a Servant that appears in Fate/Extra CCC. He is a poison-tongued, pessimistic shota writer. His Master is Kiara Sesshoin.
Although his class is Caster he is usually referred to using his true name Anderson because Kiara, who has abandoned participation in the War, revealed it. Andersen appears to be a young boy around the age of 10.
Despite being Kiara’s Servant he interacts with the player from a neutral standpoint.
He is remembered throughout the world as one of the three great fairy tale authors.
He possesses no ability to fight, thus he does not take any part in combat throughout the game. His position in the Moon Cell Holy Grail War ever so slightly insinuates: “Without victory, without defeat, I am the one to judge this story.”
He has a dark nature and is a pessimistic poet who has no desire to be liked by others. Furthermore he is no longer able to see any remaining value in himself, and completely lacks the notion that he should enjoy, or is able to enjoy his life.
Although he was summoned as a Servant, he has no wish or desire. This is probably because while he was alive he was unable to obtain anything he wanted.

“Even if life had some sort of value, it would surely be far less than most people fancy it to be.”

Like this, we can see that he has a distaste for everything in the world.
However, his true nature is to be helpful to others, and if you rely on him, he will certainly live up to your expectations. Like a good author he is conscientious, and he pays attention to all the small details. In short, he is a male tsundere.
Of course, in the first place, without the desire to entertain and to please your readers it would be impossible to work as a writer.
While Andersen is decidedly pessimistic, he advocates “Live properly” and “Do everything you can to pursue your goals to the end,” and would never laugh at the hard work of others. This is what he once dreamed that society would actually typify.

Andersen’s young appearance is in complete contrast with his choice of words, and his voice is like a sword that cuts you in two.
In general he considers everything to be completely terrible, worthless and useless, so conversation instantly freezes over when he joins in. His poisonous tongue has resulted in Kiara having to step in and mediate more than a few times.
However, while he may come across as trying to seem self-important with his pessimistic views that humans are worthless, he is similar to Archer in that if you take what he says in a level-headed manner you will realize that he is simply speaking the truth. Andersen isn’t looking down on and criticizing others, but rather just revealing the fact of things in his own sincere way.
To digress once again, we originally considered making him a Tinkerbell-like, fairy-from-a-fairy-tale-book kind of character.
Extra and CCC presents both sides of the tale.1
Similar to how each of the two Lancers are related to vampires, we wanted to link Caster to nursery rhymes and make him a märchen-like character. Eventually we thought “who would think there could be such a hateful fairy,” and settled on the current version of him.

Translator’s Notes
  1. ^ In EXTRA we see Nursery Rhyme and in CCC we see the writer Anderson, so we see the front and the back (two different sides to him).
Fate/EXTRA Material: Encyclopedia of Fate/EXTRA