Familiar: Crow named Susu.
Wand: Plum wood with kitsune tail hair. Plum is the least of the 3 Friends of Winter, which represent the scholar-gentleman's ideal. (By happy accident, Sanada has a bamboo wand)
House: Willow. Yanagi is very adaptable, and his never ending quest for knowledge makes him highly informed about multiple subjects. He can often infer what a person is going to say before they say it, which makes him seem a little creepy at times.
History: ) Yanagi comes from a perfectly ordinary, middle-class Muggle family of accountants and clerks. When Yanagi was a small child, his parents sometimes thought they saw the words and pictures on his books move, but dismissed it as hallucinations brought on by tiredness. Yanagi, being observant and quite precocious, always felt that he was a bit different but thought it would be unproductive to mention it to his parents. It thus came as a huge shock to Mr. and Mrs. Yanagi when owls started appearing around the house, delivering letters inviting their son to apply for magical schools. Yanagi was of course delighted by the prospect of a whole new world to learn about, but his parents were quite sceptical about the existence of magic and rather thought the whole thing was some sort of scam. Surprisingly, it was Yanagi’s older sister who came to his defense and helped convince their parents to allow Yanagi to attend magical school (It later turned out that she had married a wizard, but had kept her husband’s magical status a secret).
Other stuff: Sanada is his brother-in-law. (Yanagi's older sister married Sanada's older brother, much to the chagrin of both families...). Yanagi also does not play Quidditch, as he considers broomsticks to be quite illogical modes of transport. This does not mean he has nothing to say on strategies, however ;D Yanagi is also very interested in trying to explain magic through muggle science...not sure this is going very well at the moment.
Clubs
...possibly Shogi/go. He can usually be found in the library.