Sora Shiun'in/Relationship

Yūya Sakaki and Yuzu Hīragi
Yūya and Yuzu Sora's first friends. Sora didn't have any friends, growing up because everyone was too focused on becoming a soldier to make any. Sora took immediate interest in Yūya after he watched his Duel against Shingo, asking him to make him his apprentice. Yūya found him annoying at first due to his constant stalking, but this quickly changed after Sora decided to become his friend instead of apprentice, and they soon became close friends. Sora then taught Yuzu Fusion Summon after she requested him to, and since then both often spent much times with each other training Fusion Summon. Thus, Sora and Yuzu formed a strong teacher-apprentice relationship. Sora initially thought that Academia's goal was more important than his friendship with Yūya and Yuzu, directly telling Yūya that they're not friends anymore due to their contradicting views. But Sora's loyalty to Academia began to falter after knowing that Reo is targeting Yuzu, and Yūya joined the Lancers to defeat them. When they were reunited, Sora revealed his true feelings that he genuinely thinks of Yūya and Yuzu as his friends and tried to convince both of them no to involve themselves with the Dimensional War, but seeing their resolve to stop the war caused Sora to be torn between Academia's goal and his friends' safety, as while he still believes that Academia's goal is righteous, he doesn't want fulfil it if it means harming Yūya and Yuzu. Sora eventually realised how precious Yūya and Yuzu are to him and couldn't bring himself to carry out his order if it means sacrificing them, leading him to finally betray Academia for the sake of protecting his friends.

Shun Kurosaki
Sora has an antagonistic relationship with Shun due to their respective affiliation are at war. Sora views Shun as his enemy, being a remnant of Xyz Dimension that he saw as nothing but his prey in his hunting game. In the midway of their first Duel, Sora taunted him of the tragedy that befell on his homeland and mocked him for running away, occasionally calling him "Xyz scum" from there on. His defeat at Shun's hand left Sora with great humiliation and hatred for the Xyz Duelist, pushing Sora to demand a rematch and obsessed on getting revenge on Shun, something that he succeeded during the Maiami Championship Battle Royal. Shun mutually hates Sora even before he knew that Sora was Academia Duelist, the main reason because he uses Fusion Deck. His hatred deepens when Sora finally revealed his true colour, and Shun mercilessly defeated him in their first Duel, attempting to change him into card if he wasn't stopped by Reiji.

Tsukikage
Sora and Tsukikage initially were not in good terms. Tsukikage held resentment and grudge against Sora for turning his brother into a card, swearing to get revenge on him. Sora was ready to Duel Tsukikage who challenged him, but he held himself back for Yuzu sake after she asked him not to and made him realised how much suffering has been indicted by Academia. Sora's change of heart led him regretful for what he had done and apologised to Tsukikage, promising to allow him exact revenge for his brother. While Tsukikage was doubtful of Sora's true intention, he agreed to tolerate him until he save Yūya under Yuzu's request. Only until Sora saved him from the Obelisk Force, making his betrayal clear, Tsukikage finally believes that Sora's regret and his desire to save Yūya and Yuzu are genuine, allowing the ninja to forgive Sora for his past actions. Since then, the two work together to save and protect Yuzu when she was captured by Roget.