They repeatedly coordinate in group battles despite belonging to different guild structures.
Klein and his guild assist Kirito during the Gleam Eyes crisis, and Klein later joins the group retrieving Excalibur and confronting major quests.
Klein repeatedly provides direct battlefield support when Kirito is under severe pressure.
Klein and Fuurinkazan appear during the Gleam Eyes crisis, and Klein later helps Kirito hold back a raid party during the Sleeping Knights operation.
They are dependable members of the same combat network centered on Kirito's allies.
Asuna and Klein fight together against the Gleam Eyes and later participate in the Excalibur mission with the same wider group.
Their clearest established connection is cooperative participation in a high-risk group quest.
Klein and Silica join the same Excalibur party with Kirito and Asuna.
Klein and Agil share veteran status and operate within the same trusted community.
Both are recurring members of Kirito's original Aincrad survivor network and later participate in group activities surrounding New Aincrad.
Their relationship is based on shared battles and membership in the same survivor community.
Klein fights beside Asuna during the Gleam Eyes crisis and later joins missions in which Asuna is a central leader.
Explore the full interactive character relationship map of Sword Art Online