Reiji Akaba/Relationship

Himika Akaba
Reiji is shown to be good terms with his mother. Both of them agree on what they are doing and are shown to have a normal mother-son relationship. Also, Himika would often call him "Reiji-san", which is a polite suffix in Japanese that address to person who is respected, showing how much Himika greatly respects her son. However, her heartless experiments on Reira's emotions have actually shown to dissapoint him and caused him to slightly resent his mother.

Reo Akaba
Reiji considers his father as an enemy, disagreeing with his goal to unite all four Dimensions. Whenever the subject about his father's goal is brought up, Reiji clearly showing his anger, as oppose to his usual calm demeanor. It is unknown how Reo feels about his son, but Reiji stated to Shun that he doubts his father would care about his well-being.

Reira Akaba
While Reiji and Reira aren't as close compared to other pairs of brothers in the previous series such as the Kaiba brothers, they still are shown to care about each other. Even though it is later revealed that they aren't related biologically, Reira admires and looks up to his older brother, referring him as "Nii-sama" in Japanese. While he is very shy and reclusive to others, even to his to own mother, he seems comfortable whenever Reiji is around, as shown when he Dueled Ayu; he at first reluctant Dueling her, but when he saw Reiji watching his Duel, Reira quickly became more focused on winning, showing that he doesn't want to disappoint his brother. Reiji has high hopes for Reira, though he is not as strict as Himika, complimenting and patting his head when he won. Reiji is also confident with Reira's Dueling skill when the others doubted him, defending Reira when Shun and Shingo objected his participation in their trip to Synchro Dimension. When the Lancers were split in the Synchro Dimension, Reira only cared for finding Reiji as soon as possible, and Reiji requested Tsukikage to find Reira and later to take his place in the Friendship Cup. When Reira showed signs of developing a "sense of self", he was shown to be proud and seemingly resents his mother's plan of using Reira as a mindless puppet.

Yūya Sakaki
Reiji developed a quick interest in Yūya, the founder of Pendulum Summoning. Despite there are many talented Duelists, Yūya is the one who he has his eyes on the most. He asked Nakajima to observe and report any progress on Yūya's Duel and even asked for the Duel Committee to permit Yūya into entering the Championship despite lacking the condition to enter (Yūya refused this offer though). Although being one of Yūya's rival, he doesn't show any dislike towards him and even defended him when Mr. Sawatari accused Yūya as the culprit behind Shingo's attack. Although he views Yūya's resolution is naïve, Reiji doesn't stop having high hopes for Yūya due to his growth, going as far as to provoke him during their rematch to make Yūya join Lancers since he is necessary to fight the Fusion Dimension.

After their first Duel, Yūya quickly views Reiji as one of his rivals and strives to grow his Pendulum Summoning not only to become the best Pendulum Summoning Duelist but also to defeat Reiji. Yūya at first respected Reiji as a great Duelist, but any respect he has for Reiji quickly fades after he learned that Reiji purposely held Battle Royale to test which Duelist is suit to become part of his Lancers, making him partly responsible for turning most of Battle Royale Duelists into cards.

Nakajima
Nakajima is Reiji's closest subordinate. Nakajima is shown to be very loyal to Reiji, obeying his every order and dedicate himself to accomplish it. Reiji also trusts Nakajima to do his work, personally asking him to give report of any activities concerning Yūya or cases happening in Maiami City to him.

Shun Kurosaki
At first, Shun was targeting LDS in order to capture Reiji as bargaining chip to save Ruri, but they then work together after knowing they are sharing the same goal to defeat Reo. They're not in a really good relationship due to their differing ways of handling the situation, though Shun mostly relents to Reiji's order, knowing that his plan is for the best, despite his own reluctance.

Serena
When Reiji met Serena in the Fusion Dimension, he tried to help her escape without hesitation. Despite knowing Serena's alliance to the Academia, Reiji trusts her and plotted to have her to join the Lancers knowing she wouldn't betray them. Serena likewise accepted to help Reiji combat the Fusion Dimension and supported his plan to go to the Synchro Dimension to recruit allies.