Chikusa is constantly bickering with Ken due to Ken's mockery towards him. Ken calls him "four-eyed kappa"; sometimes Chikusa is patient and just ignores this, and sometimes they begin to argue. Whenever Ken tries to act reckless or stupid, Chikusa always stops him and apologizes on his behalf for his idiocy (on the Ken Bam-Bam channel, Chikusa apologized to Mukuro for Ken's stupidity when Ken makes him his guest). He likes to points out Ken's pranks to Mukuro such as when Ken compared Mukuro's or Chrome's hair with pineapple or when Ken lied that he feed Chrome properly while in reality he only fed him chocolate meals, which resulting Ken being punished by Mukuro. Aside from this, he also likes to tease Ken of his dishonesty for Chrome's well-being, which Ken hotly denies. Despite this, however, both could be considered as good partners and childhood friends. Both will work together when the situation demands it, especially whenever Mukuro or Chrome is involved. In an anime flashback of his time in the Estraneo Famiglia when Ken and Chikusa intend to check the room where Mukuro killed his captors, Chikusa hid behind Ken out of fear. This may hint that Chikusa used to rely on Ken when they were children.
Like Ken, Chikusa displays great loyalty for Mukuro and is ready to sacrifice himself for him. Mukuro had saved him and gave him a place to go just like when he desperately tried to help him when he was defeated by Tsuna despite his grave injuries. He doesn't mind even if Mukuro is just using him and obediently carries out his orders. He also always reports to him if Ken starts to pull some pranks and helps Mukuro to punish him, much to Ken's anger and dismay. (In Haru's Haru Haru Interview: Dangerous, he helped Mukuro cut Ken's hair into a pineapple hairstyle). Mukuro acts indifferently towards Chikusa, though due to Chikusa's calm nature, Mukuro seems less talking to him than Ken. Despite claiming he and Chikusa are just tools, Mukuro actually tolerates them and even sacrificed himself for them to be imprisoned in Vindice Prison. So far, Chikusa is the only one of Mukuro's subordinates who's shown to able to restrain him when he loses his temper.
Similar to Ken, he has some concern for Chrome's well-being but never shows it openly. Whenever Ken starts to shout at her, Chikusa always stops or restrains him before he can go any further. He is also fast to realize if something is wrong with her, like when Chrome returned upset after being taken by Demon Spade in the Primo Family Arc. He also pretended to not understand who Ken meant when Ken asked about her whereabouts by referring to her as "stupid" or "ugly girl", and only responded when Ken finally used her name, implying that he has a certain degree of respect for her. Chrome regards him as one of her first comrades along with Ken and holds him dear to her.