name: Kuzuki Souichirouage: about 35 years old
nationality: Japanese
profession: teacher
family: nobody.
likes: staying by himself, planning in the shadows, killing people
dislikes: being controlled by others
magic powers: Unknown although he has a sort of assassination skill.
servant: Caster
personality: Souchirou isn't a very well described character. He appears as someone who's always trying to hide something, from his past, from his present, someone who's not able to express his feelings, understanding them or even trust them. He doesnt' get along that well with others and he always tries to avoid contacts with anybody. He enjoys pretty much being alone and the only person he seems to care about is Caster, who was saved by him just before disappearing because the loss of a master. They were in love and they didn't either try to hide it, adding a bit of drama to their BG and generally to the story itself.
spoilers warning!!!
personal story: We know for sure that Souichirou was an assassin before becoming a teacher. He was raised as a killer since his childhood with the aim to kill a single target in all his life. When he successfully accomplished his mission, he found out he had nothign else to do in life. He than decided to look for a meaning for his own existence and that's why he left the organization he was part and wondered around, stopping at Fuyuki City and trying to run away from himselg He found himself at Ryuudo's Temple and ended up in asking to the monks to be accepted as a host there, He tried to change his lifestyle and become a teacher, trying to bury his past, withouth any significant success. He soonely meets Caster, who is looking for a new Master and he gladly accepts to become hers. He's involved in the Holy War and he tries to collect a large amount of mana, togheter with Caster, in order to become more powerful and get the victory. As Caster is defeated by Saber, he doesn't loose his will to fight (probably because he promised to Caster he would keep on fighting for their aim or maybe because, loosing his love, he has nothign else to protect in his existence) and he tries to defeat Shirou with his own strenght. He fails once again and, despite Shirou's doubts on his real intentions, he's killed by Archer.