Suzu acts as Mary's guardian throughout most of Mary's early life. She was appointed by Mary's father to take care of Mary after Mary's mother was abducted and pronounced dead.
Suzu appears as a loyal and trustworthy figure who would stand up for Mary in any circumstance. She always seems supportive of Mary and would mostly agree with any idea Mary would come up with. Suzu's mind is always on her mission to protect and support Mary; she has a strong sense of duty.
Suzu's weapon is a scythe which consists of half a scissor blade attached to a stick with some sort of gem, presumably an emerald, as a counter weight. Her attacks are short range melee attacks which deal a lot of damage but are limited in range and speed.
In one of Suzu's notes (located in her bedroom), it is explained that the wedding ring, she wears around her hips, is a symbol normally associated with women of the night. Though not directly addressed, it is presumed that Mary's father had developed some sort of relationship with Suzu after losing his wife.
Suzu's note also explains that she still retains the ring as a new symbol of her eternal bond to Mary and the oath she made to protect her at all costs. The note specified that it would be very difficult for Suzu to remove the ring even if she wanted to do so, due to various obstructions above and below the ring.
This provides some insight into Suzu's past profession and explains why Suzu was not surprised or mystified by The Bar, as she most likely was already aware of its existence.
Relationship with Drake
It is not clear if Suzu and Drake had some sort of relationship, however in various interactions with Suzu, Drake had complimented Suzu on her appearances and acted flirtatiously around her.