Xi is pretty harsh and indifferent, sometimes known to be cold or heartless. He often acts formal with a stoic face. However, his true emotions shows out due to Jinghua's innocent and sincere personality.
Duanmu Xi bears a striking resemblance to his own ancestor Duanmu Luoyue. Ironically, the soul image he chose Yang Jinghua's true form bears a physical resemblance to Luoyue's student Yang Ning, also known as Yang Zicheng. This causes some confusion to spirits as it seems that even in a millennia, the fate of both bloodlines still cross.
Duanmu Xi is referred as a "handsome Korean- actor look alike" by Yang Jinghua in the Chinese animation. In the anime adaption he is typical attire consists of a long-black hoodie, white button up shirt, black tie, black jeans, and a blue and black stripped scarf draped over his shoulders. In the manhua he can be seen with several different attires.
He has white hair with white eyes in the manhua and brown eyes in the anime. In the anime his hair is slightly different with it kept short with two long bangs framing the sides of his face.
In the manhua Duanmu Xi is often shown with a cigarette and tends to smoke most of the time but this was taken away in the anime.
Duanmu Xi is a formal and calm when around others, and does not involve himself with small affairs, however when he is alone or around Yang Jinghua, he will show a softer, more gentle side of himself.
Duanmu Xi's half brother Duanmu Siming also points out that he has only ever seen the man smilingly blissfully in front of Yang Jinghua.However he can also appear to be quite heartless as shown when he fired Duanmu family's butler (in the anime adaption as this was not in the manhua), who has served them for a long time, after his son almost killed Yang Jinhua even though the butler begged him to forgive both his son and himself for the idiotic acts caused. According to Yang Jinghua he is also quick witted and quick to solve problems. This was shown when Siming and Siyun along with the Situ family blamed Yang Jinghua for using the Luoyue sword without permission to hurt Situ Iv. He silenced all of them when he gave the sword to Yang Jingua to use it as his own.
He can seem stern, stoic and mature above his age due to the role he has to play as the master of the Duanmu household but in actuality, he is a normal teenager, and that side of himself is revealed several times in the manhua.
He is also shown as a sleepy head who is always sleeping if not eating. This seems to irritate Yang Jinghua as the former does not tend to get fat even with his lazy, inactive schedule. But the reason behind him doing so is that his life span is running out, causing him to become tired very easily.
Yang Jinghua/ You Keika - Yang Jinghua/ You Keika (in Japanese) is the spirit shadow/ soul image of Duanmu Xi. He was chosen when he was hit by a truck and died on the spot. Duanmu Xi convinced Jinghua to be his spirit shadow when he the told the latter that he will disappear within the seven days of his death or be turned into an evil spirit.
Duanmu Xi is shown to have a very gentle and caring side to Jinghua, often saying that he is the one thing that is important in Xi's life and the precious person he holds dear. He was visibly worried and unhesitatingly showed it when Jinghua told Xi that his soul was almost ripped apart by Situ Iv. Xi yelled at him and told him that he should have called him. When an irritated Jinghua yelled back that he called for Xi several times in his head, Xi was flustered and even blushed at the fact.
Xi is able to sympathize with Jinghua at the fact that he knows what losing parents feels like and stated that he wanted to be Jinghua's family (in the anime).
Xi goes to great lengths to protect Jinghua. Giving him a new set of clothes to protect him from other powerful spirits (only seen in the anime, as the blue clothing is his new attire in the manhua) and sacrificing his own life to safe his spirit shadow. He also cares a lot about Jinghua's feelings and emotions to the point where, while he was wounded and healing, he drove Jinghua to his home town on the seventh day of Jinghua's death, so that the boy can express his feelings and visit his friends one last time.
Xi and Jinghua's relationship is a running gag in both anime and manga as a "married couple" because of the soul contract that binds them both together for life. The ceremony for the contract is even similar to a wedding where they pledge their vows to each other.
Qin Shiyao/ Shin Shiyou - Qin Shiyao is meant to be Duanmu Xi's fiancee. They were arranged together by their family as she has a special body type that can heal Xi. Althought Xi seems to be cold around her, he can also be seen caring for her in the manhua.
Great-grandmother- She is the grandmother of Xi. She was the one who chose Xi to be the head of the household solely because of his powerful spiritual energy and his skill that far besieged the talent of the actual two members of the Duanmu family.
Duanmu Siming- Duanmu Siming is Xi's half brother and his personal secretary.
Shenlong Zhangxuan- Shenlong Zhangxuan was the bodyguard and best friend of Duanmu Xi.