Blood
People with the bloodtype B are classified as "hunters". They do things their own way, have strong personalities, and are optimistic and cheerful. They are also generally adventurous, sensitive, and kind. However people of this bloodtype also express forgetfulness, indecisiveness, and are prone to being noisy, messy, and disorganized. They also have a habit of exaggerating.
I have to say, Yuuhi definitely seems a type B person. He's optimistic and cheerful, he has a strong personality and is very sweet and kind. He certainly seems to be the adventurous type, though that's mostly due to unavoidable circumstances he'd rather not be a part of. All he really wants from life is to find a girl and settle down.
He also seems to be noisy: he likes his music loud and doesn't mind getting into a yelling match with Suzumi or Aya.