The two have very little interaction in the canon main plot, with the only one being when Korekiyo asks Rantaro how he wants to accomplish ending the killing game. However, they have more interactions in the bonus content.
During his first Free Time Event with Kaede, if the player chooses to talk about Kiyo, Rantaro tells Kaede that Korekiyo has a strong personality, but if she takes the time to speak with him she'll understand him. In addition, he emphasizes that Korekiyo is a calm person who seems to be a clever type.
The two also have two events together in the bonus mode, Ultimate Talent Development Plan. In these events, they bond over both of them traveling a lot, their knowledge about various cultures and having sisters who are important to them.
- “"Oh yeah, talk about first impressions...But you know, he isn't so hard to understand if you talk to him a little. He's always calm, and he seems pretty sharp. I think he could end up being pretty reliable."”
- — Rantaro about Kiyo in the optional dialogue of Kaede and Rantaro's first Free Time Event.
- “"Kehehe...oddly enough, when I look at you, I sense that we are kindred spirits. You, too, are flitting around with a purpose... That is what I have deduced."”
- — Korekiyo about him and Rantaro being similar, in their Friendship Event from the Ultimate Talent Development Plan.
- “"Kehehe... Is that so? I won't ask in detail, but I shall root for you."”
- — Korekiyo after finding out Rantaro has a little sister, in their Friendship Event from the Ultimate Talent Development Plan.
The two are shipped together mostly as a result of the similarities between them that are pointed out in the Ultimate Talent Development Plan, with both of them having sisters who are important to them, traveling a lot, and possessing knowledge about various cultures - Rantaro as a result of traveling and Korekiyo as a result of being an anthropologist.