"If I am indeed selling you out, please feel free to show this chat log to the teachers, Manabe-san. This account has been registered with the school's phone. In other words, I'm risking my identity to take revenge on Karuizawa-san. That way, I'm the one bearing the most responsibility. Isn't that right?" I told her.
I'm sure Manabe also understands this well. Even if this is a sub account, once you analyze it thoroughly, the identity of the person behind it can be revealed. If it comes to that, I, as the one who masterminded this plan for revenge, would bear the most responsibility and undoubtedly be punished harshly. "Then if I show this chat to the school now what would you do, it's over for you" Manabe asks me.
"Because I believe Manabe-san is not the type of person to do that. I must trust in order to be trusted after all" I told her. "I understand what you're trying to say, more or less. I'll hear you out at least" she finally said.
After that I repeat a similar story to her multiple times over. About how much I hated Karuizawa. About how I wanted revenge on her yet couldn't as someone in a weaker position. And about how I overheard how Manabe and her friends were quarreling with Karuizawa. I thoroughly made sure to play the victim.
"Once we return to land, contact with Karuizawa would surely become difficult. Since the school dorms are littered with surveillance cameras, even if you tried to bring her into a private area, there would be eyes watching you. This place, a battlefield with no escape, would be the perfect place for you." I told Manabe. This would make sure Manabe and the others realize this place, only on this ship, can they get their revenge. "So...what are you proposing you can do?" she finally asks me.
Manabe, who seems to have finally caught up with my plan, finally starts asking questions.
"I can call Karuizawa-san. After that, you can take your time talking with her and settling the problem" I told Manabe.
And with that, through the chat, I sent her a map of the lower levels of the ship.
"Since phones don't get reception down there. She can't call for help either. And no one normally goes down there anyways" I said. "I see...so you can call Karuizawa-san down there as a classmate?" Manabe asks. "I would like you to decide now whether to cooperate with my plan or not. After I call her, you can decide whether or not you'd like to have your revenge. There would be no problems that way, no?" I asked her.
After that, for the longest time, despite the 'read' sign having appeared. No reply came from Manabe. Then. Once the reply came, I became sure I would succeed. IF my plan to convince her via chat failed, I had another plan prepared where I would have to appear before Manabe myself via direct contact. Of course that was dangerous. Since I had taken several pictures of her threatening Karuizawa in the emergency staircase, I could have blackmailed her into following my plan. But the risk is also massive, since I would like to avoid my existence standing out.
"Now. Let me see what you can do, Manabe".