Prisoner 24601
You wake up in the room allocated to you. It is simple, furnished with nothing more than a cot. It has only been a day and already you are tired of the restrictions. Everyone here began with a karma of zero, apparently representing a clean slate for a new life.
Complaining loudly about the food – no meat whatsoever, only a greenish mash of unidentifiable plant material – had earned you a deduction of twenty points off the bat. Attempting to intimidate the cook into finding something more appetizing in the kitchen, that was sixty points gone. Cursing the system out loud was worth another twenty, giving you a total of negative one hundred points by the end of your first day.
“Tardiness in the morning. Deduction of ten points. An active start to your day is the best way to cultivate a healthy lifestyle,” lectures the androgynous voice in your ear. It looks like you would be getting further reductions to your karma the longer you stayed in the room. Grumbling, you get moving, dispelling the invisibility spell that you had hoped would work. At least this has taught you something: the system is always watching.
Out in the corridor, you meet Rin, who looks equally disgruntled. “Top of the morning to you, 24601,” she says in a forced manner with a ghastly smile that seems to have been hammered onto her face with nails.
“Top of the morning to you too, 24602.” Then you looked at the young girl at her side, still mute and expressionless. 24603: she too had been assigned a number and a room. You had passed her off to Rin as soon as you could, seeing a good opportunity to be rid of the responsibility for a while.
The prince’s double. There was little other reason she would be dressed up as the prince, as according to Rin’s report, the real prince had surfaced a while after you left. You have no idea why his double would be a girl, but for now it is a question you do not have time to ponder. As for the others, you know little more than you already had. Rin had hurriedly come for you immediately after teleporting them to safety and ascertaining that you had not appeared where you should. She had not expected to be trapped here, but there is nothing either of you can do about that at the moment.
As you engage in morning exercises in the courtyard, never taking your eyes off Rin’s stretching activities in front of you – “Visual harassment, deduction of ten points,” – you consider your next move. There was a clause that allowed an inmate to challenge residents of the higher floors for their place. The clause’s presence itself feels strange to you; why would a place purportedly aimed at the rehabilitation of its prisoners have an option for a shortcut?
No one else questions its existence, however, and you are not the sort to let an opportunity for the quick route to slip through your grasp. There are seven floors in the tower. From what you know, inmates of the upper floors are allowed access to every floor below them, but the reverse does not hold true. When you make a challenge, however, you are allowed to challenge anyone whose identification number is known to you.
That means you can go right for the heads of the most famous inmates in the tower, should it strike your fancy.
The highest ranking resident whose number that you know would be the current head of the guards, the self-proclaimed Warden of the Tower, number 4799. He is a demon who is amongst the oldest denizens of this place, and coming out victorious over him would catapult you to the sixth floor immediately, regardless of your karma.
If you lost, however… well, no one seemed to know what happened if you lost. At least, no one on the first floor. As far as the prisoners were concerned, challenges only happened in the upper levels, when they had successfully worked their way to more benefits and less restrictions on their natural abilities. It soon becomes clear to you that information about this clause is also purposely restricted by the residents of the upper floors. What little has trickled down has been kept vague and threatening. The Warden aside, all of the guards that patrolled the lower levels have had their numbers concealed. But the clause exists in the system nonetheless, and you plan to exploit it as best as you can.
At the moment, your fellow inmates are willing enough to talk to you, but without more concrete proof of your ability they are not willing to contribute anything more than shallow gossip.
You will have to take the first step.
***
A. You challenge No. 20117, Salamander. A fiery lizardman who is considered one of the more influential prisoners on floor two, he will serve as a good stepping stone for the upper levels. Being on the second floor also means that it is relatively easier for you to gather information about him as compared to targets residing on the upper levels.
B. You challenge No. 24003, Queen Bee. Floor four is said to be a gathering of the strongest inmates, and they are divided into multiple factions each seeking to raise their own karma and decrease that of the others through constant schemes and conflict. Being a recent convict who has risen quickly through the ranks to lead a faction of her own, Queen Bee’s number is still fresh in the minds of those that are willing to talk to you.
C. You challenge No. 4799, Warden. If you’re going to do this, you’re going to go all the way to the top as quickly as you can. You are certain that you can find a way to triumph, one way or another.
***
1. You perform the challenge yourself. Building your own reputation is important.
2. You have Rin do it. It is easier for you to operate in the shadows if she attracts all the attention.
I guess it also explains why they didn't mind Erd's bare body nor bothered to give him anything: in spite of their rules and everything else, they still have their... "Needs". 
