Vocaloid 02, A mirror image of Rin Kagamine.
Len is very protective of his sister and is usually around her to she if she doesn't get hurt. He can, though, be very childish and stubborn, but is serious when he needs to be.
Rin and a ...Banana?
In his past life, he was a very handsome boy with his twin sister that he served her every whim. He had fulfilled all of her wishes and done all she asked, soon causing the kingdom to riot. In an attempt to save Rin's life, Len sacrificed himself by dressing like the princess and being beheaded in her place.
In his current life, he had been built as a robot, in the mirror image of his sister, Rin, who had died, and been created after him. Now they live in the house, no memory of the past life, but still just as happy together as they would be if they did.