Admittedly, falling for a prisoner as a guard wasn't the best idea. It's not like you can control who you fall for though. You were a guard in building 3, you'd often be tasked to go to other buildings to give or take paperwork for Kiji, or do other jobs like that. Despite not being deputy, you still didn't a lot for Kiji seeing as you were the closest to him. Since you two were so close, Kiji noticed how you've become slight distracted, especially you asking to going to building 5 often. He wanted to know what was going on so he asked you if something was wrong.
So, you told him about your likeness towards a specific inmate in building 5. How you met him, Kiji didn't know. He was surprised to hear Ruka's name. It had been a while since Kiji had seen him, probably not since Ruka got locked away. He wasn't going to shame you for liking Ruka, he too could admit Ruka was one to like- to a certain degree. But a guard and an inmate wasn't allowed, especially one that was in the underground prison. You knew this but you still hated it.
After speaking to Kiji about this, you wanted to see Ruka. So you did. Though, now that Kiji knew, you knew he wouldn't let you back to building 5 without someone else or himself with you. But, a little lie wouldn't hurt, right? You told Kiji you were clocking out and heading off but here you were, in front of a smirking Ruka.