Ship Leesoo: These two get along well. While Hatsu didn't want to associate with Anak anymore after the teams dissolved, he still socialized with Leesoo. They went friend hunting together, trying to fill up their friend list. Leesoo often acts as the glue and mediating force between Anak and Hatsu.
Later in Part II, their bond and trust have improved significantly. The two stuck together throughout the 8 years, giving each other complete trust since.
Anak Zahard: These two do not get along and often disagree on things. While Hatsu tolerated her selfish actions to a certain point when they were on the same team, he didn't wish to be associated with her anymore after the teams dissolved. Ship Leesoo is usually the reason why they can get along.
Twenty-Fifth Baam: These two are good friends. Hatsu seems to like and appreciate Baam's honesty and desire to help others, regarding their friendship highly. They can sometimes be seen socializing outside of tests. Baam has helped Hatsu fill out his friend list. Hatsu is quick to defend Baam and was angry on Baam's behalf when it appeared that Khun was abandoning Baam. When Baam was thought to be dead, Hatsu was the one to propose helping Rachel because he felt he owed it to Baam.
Khun Aguero Agnis: These two are friends, though they like to make fun of each other. Hatsu calls Khun "ear decorations" and Khun in return calls him "halbok warrior". They are often able to get a rise out of each other. Though Hatsu was the one to propose helping Rachel, he seems to follow Khun's lead on how to do it, letting himself get separated into another team.
- Vol.2 Ch.249: 43F - Hell Train: The Floor of Death (18); Blog Post
- SIU Private Blog
- Ch.30: 2F - Position Test (3)
- Compilation of all additional materials (2011)