Reiji always dresses formally, with shirts and ties tied tightly so that it matches his serious personality. Reiji's uniform, like the others, consists of a black jacket, black pants, and black dress shoes. He wears a red velvet vest and a neatly tied tie of the same color. In More Blood, he wears a black military-style coat with a white shirt suit underneath and black pants.

Reiji is characterized by having very good manners, a very refined and sophisticated way of speaking; for this reason the creators liken him to a high-class butler, however he is still very strict. If one does not take into account how harsh he is, one can see that he has a certain sense of humor deep down. Although Reiji is the second son, he is the one who cares the most about order and discipline among his siblings in the Sakamaki mansion. If you add this to his manners and refined personality, it makes it seem like he is the eldest son when in reality he is Shu. Reiji loves values and rules, which makes him a very strict person not only with his brothers, but with himself as well. He is an arrogant and very proud person, so much so that he hates to accept when he makes a mistake if he ever makes one since he is too much of a perfectionist. Also like his brothers, he is sadistic; he tortures for fun. Reiji is the one in charge of cooking and cleaning. This love of order is sometimes used against him by his brothers so that Reiji cooks for them, thus preventing them from touching the kitchen and destroying it. Aside from his passion for experimenting and creating different potions and drugs, he also loves collecting sets of mugs and fine tableware.

Reiji is the second son of the Sakamaki family. Because his mother Beatrix was Karlheinz's second wife and gave birth to the family's first son, Shu, he was mistreated a lot by Cordelia since she was the first wife. For this reason, Beatrix focused all her attention on Shu to transform him into a worthy heir of the family, completely neglecting Reiji. However, while Shu hated being given so much attention and being restricted from certain things, Reiji was dying for him to receive some of that affection as well. This caused Reiji to kill Edgar, Shu's childhood best friend, by burning down his house. He kills Edgar in order to get Beatrix to notice him and because he resented Shu being given so much attention when he ran away from his responsibilities and his attitude left much to be desired, making Cordelia angry. As his plan to kill Edgar didn't work, and even Shu and Beatrix's attitude didn't change one bit, Reiji hires Seiji, who was a vampire hunter (he would become Yui's father) to kill Beatrix so that his mother would finally recognize him. Unfortunately, all this accomplished was to make Reiji grow resentful, as Beatrix in her final moments dies with a smile knowing that she will no longer be tormented by Cordelia and witnessing Reiji's growth.

Siblings. His relationship with his siblings is generally not very close. Reiji only tries to uphold the manners and rules imposed on him by his father. However, his siblings often just make fun of him. Shu Sakamaki. Since Shu rejected all attention from his mother and even ran away from his responsibilities and did nothing productive, Reiji has a great hatred and resentment towards him. Reiji is the culprit of the fire at Edgar's house, which traumatized Shu considerably, however Shu until now does not know how the events happened. Reiji usually calls him: good for nothing (穀潰し Gokutsubushi). Beatrix. Reiji admired his mother as a child, seeking her attention, but she didn't give it to him and Shu gave him everything. This caused Reiji to grow up with hatred and jealousy towards his brother, secretly thinking that he was secondary, just because he wasn't the firstborn. His mother's neglect in making him a servant of her brother pushes the intelligent and ambitious Reiji to be capable of committing real crimes, while fully understanding the consequences. Reiji sees his mother Beatrix as the 'Perfect Woman' and when he sees her collapse in front of Cordelia, he loses his respect. In part, he still tries to create more or less a perfect copy of his mother in Yui. Karlheinz. Reiji has always admired his father, even though he also neglected him too much. Reiji always wanted to gain his recognition, making him the only one who does not hate Karlheinz among the Sakamaki Brothers. For Reiji, the greatest compliment that can melt his heart has to come from his father, and even if he realizes all the evil his father has done, Reiji blindly accepts it as something necessary and good. In Dark Fate, Reiji obtains Karlheinz's power and recognition, even trying to imitate him as his way of expressing himself, acting, and even letting his hair grow long. In his childhood, Reiji received a gift from his father, a pocket watch.

Teleportation. Reiji can appear anywhere out of nowhere. Telekinesis. He uses his power to move Yui's hand. Fly. Vampires have the ability to fly during the full moon. Fencing. Reiji is talented at swordsmanship, as seen in Shu's 3rd ending in Haunted Dark Bridal. Others. As he is a pure vampire from birth, he can only die if he is decapitated, however, if his body is too badly injured to heal quickly, it is potentially fatal, but not directly so. One of his passions is making poisonous potions. Reiji has basic knowledge of healing/treating vampires.

Reiji is right-handed. He has purple boxers. He has great cooking skills. He knows all his siblings' favorite foods, except Subaru's, since he doesn't have a specific one. He is an excellent cook. He has a collection of porcelain cups, which he calls "My precious children." His foot measures 27 cm. He wants all his younger siblings to like and admire him, especially Subaru; Reiji is concerned that he is a kind person and hides it all with his bad attitude. According to the Drama CD "Vampire Juice ☆ Year-End gift", he seems to be the type of drunk who is too sensitive, Reiji "educates" Yui to be a perfect copy of her mother. When Karlheinz died on Reiji's route, Reiji began trying to imitate his father's attitudes and expressions. Reiji speaks fluent German, knows how to play the piano, and is very good with the sword. He is good at chess. Its lens measurement is 0.5. He's afraid of ghosts, since they have no scientific explanation and he can't find any. He tends to be like humans; he's afraid of the unknown. Reiji means "kind child" Cordelia said that Reiji is very handsome. Reiji likes roller coasters.

He's usually seen alone and doesn't care much about what's going on around him; he's the quiet type who doesn't like company. However, he gets easily annoyed and becomes very violent, to the point of breaking and destroying everything around him. The good thing is that when he's with you, he can control his temper. There's even a tsundere side to him that only you and his brothers are able to see. He's also a 'delinquent' type, as he's somewhat violent and likes to break things. Subaru is also sadistic like his brothers, but sometimes he can be sweet and somewhat kind, like when he tried to help you escape the mansion and even gave you his silver dagger, which is capable of killing vampires. Multiple images show him playing the piano, although this hasn't been confirmed in the series yet.