"Because... hm... never mind."
"Now you're making me curious."
"Ugh, it's not uncommon for Noir members to temporarily or permanently switch to IHPS. You know, like Niel—Instructor Niel. He used to be in Noir and changed his identity to go into hiding. I mean, my suspicion doesn't have strong evidence, but... sometimes Noir members infiltrate other organizations to spy, whether on their methods or the people working there. And looking at you, there's nothing special about you to make someone spying on you, though..."
"... Wait, if you know about that, IHPS must know too, right? That Noir members aren't one hundred percent 'innocent.' So why does IHPS still accept them?"
"It's like eating each other." Marcus replied succinctly. "Put it this way, if both organizations are harboring criminals, there are people who want to catch those criminals. So they investigate each other, like a competition."