Shun Kurosaki/Relationship

Ruri Kurosaki
The two are siblings, and seeing from Shun's determination to find her, they had a close relationship. He goes as far as to target LDS to bargain Reo

Yūto
Shun and Yuto appear to know each other for along time. Although there have been disagreements and differences between their ideas, they have a lot of faith and trust in each other. Yuto refers to Shun as his best friend, protesting that the two did not 'run away' from their homeland, while Shun shows concern when Yuto fought with Yugo when a Synchro Summon was detected.

Reiji Akaba
Despite previously being opposing forces, they team up for their own gains. Shun had hoped to bargain Shun for Ruri, but ended up joining LDS to find more opportunities to find Ruri. In turn, Reiji has Shun inform him on what his father is up to. The two share a common goal, to find Reo Akaba and know what he is up to.