Luna was confused and scarred from what was happening before her. He had warned her that he would show her an invisible attack that could kill her and that if she didn't help him calm his sister after that he would kill her. At the time Luna had thought that those were empty treats but as she watched this prince Blue Blood be dispatched she began to worry.
{He will attack. Will he attack our sister? No he promised he wouldn't not yet at least. Then that means that he would attack the guard, but if he does our sister would never listen and will imprison him, and-and then he would kill her. What do we do? How do we stop him. If we kill him our body will shatter and it would take me eons to craft another without the aid of the elements. No we wont let our sister suffer because we couldn't control this human.}-As Luna frantically thought this she heard the sound of metal breaking concrete behind her as a single loose tennis racket string hit her ear. {Oh no did he attack our sister. Please no!}-Luna thought as her eyes met Nights his eyes holding noting but the resolve to kill even if it cost him his life.

" If I wanted you dead that badly you would be."- At the sound of this statement Luna was relieved. He had attacked her. Celestia and her subjects were safe. She was so happy she could faint but then she watched as Night headed over to Blue Blood and held a sword against his
trembling and wounded body. Worry and panic began to come back to Luna's mind.

"I Surrender"- As Celestia heard this she was snapped from her shock. Night Shadow had attacked her sister and spoke of killing her.

"Guards restrain him"-Celestia ordered but only a few moved and even they froze once they met Nights gaze.

{Oh no we must stop this before it gets out of hoof. But how he attacked us. Our sister would need explanations she believed that he truly loves us. Why would someone who loves you attack you.}-As these thoughts raised trough Luna's mind. Celestia had taken it upon herself to fly over to the ring and was now staring Night in the eyes. Neither one of them moving waiting for a sign that the other is distracted before they begin their attack.

{Aha this will work it has to.}Luna thought as she teleported her foal body between Night and Celestia. She then faced her sister and spoke.

"Sister forgive us for causing this disturbance. Night and We had a personal argument and we believe that in his desire to prove he was correct he may have caused thee all worry."-Luna then turned to Night as her sisters jaw dropped. "Thee have proven thy point."-As she said this Luna noticed the intent to kill disappear from Nights eyes and continued to speak more calmly. " Lower thy weapon and trust that we shall let no harm come to thee for what transpired here."

Everypony was shocked and relived at how Luna had made Night give up without a fight but as some guards stepped forth to restrain him she spoke again.
"We shall not allow Night to be restrained. He did noting wrong but attack the wall of our stage and even then it was with good reason."- As Luna's horn began to glow to keep the ponies from starting a fight she would regret Celestia came to her senses from all of the shock.

"Sister you must explain of what this argument was and how exactly did Night make a point by attacking you? As you stated that it was personal I will not make you tell me here but I must ask that Night be confined until I have heard the reasons.""-Celestia said sternly.

"Sister you cant he broke no rules of the challenge and as he stated had he wished to I would be dead."-Luna attempted to argue knowing that should somepony try to imprison him Night might lash out and kill them and then it would be just a matter of time before she would have to watch her sister lose her body or lose her own.

Celestia thought for a moment as she looked around Luna had a point, but Night was too dangerous to be left alone while her sister explains what happened. She exhaled deeply and then spoke calmly.
"Very well sister. You shall explain to me what happened in your quarters and Night is entrusted in your care until I deem that he may wonder the castle grounds alone."-Celestia stopped for a moment as her sisters horn stopped its blue glow.
"Guards as todays test has shown clearly to me that it is unfair for just 5 ponies to stand against Night Shadow starting tomorrow he shall be facing groups of 10.However as none of the rules I stated were broken my sister now has her first 5 royal guards. As Night has demonstrated even if you fail the test you lives shall not be in danger but should you wish to serve my sister but are still afraid of the test you can surrender at any time as Night said during his duel. There shall be no more tests for today as I have matters to discuss with my sister and Night Shadow."- As Celestia said this she put emphasis on "royal" and "duel" but attempted to sound as calm as she could.

When Celestia finished her horn lit up and she Luna and Night Shadow were teleported to her sisters bedchambers before any pony could argue or question what she said.

"Now you two explain how is Night claiming that he can kill you Luna prove any point other then the one that should be restrained?"-Celestia asked sternly looking at her sister and Night.

Night acted as a foal that was caught with its hoof in the sugar cube jar before dinner looking at Luna for answers and not speaking. Luna on the other hand stood up as tall as she could and spoke.
"Well sister after the morning breakfast Night and We argued. We believed that he would kill us if we did not possess magic to control him and the only reason he had stayed with us and suggested this challenge was because he feared that we might smite him should we grow bored of his presence. He claimed that if he truly did not wish to stay by our side he would have ended both our lives magic or not and furthermore stated that while we bound him he still considers his skills his own and to serve his own desires and that he would lend his aid to us of his own will should we ask it."-Luna stopped to let her sister proses the information before continuing. " Even thou his words were sound we did not believe them after all why would he lend his aid to us if we had taken his freedom and bound him with magic. Upon our continued argument Night claimed that only actions shall convince us that he is not acting out of fear of our magic and claimed that he shall demonstrate his resolve. We do not approve of the way he went about doing it but it did convince us of his resolve and that he was not afraid of our wrath and is truly serving us of his own will."- Luna finished and waited for her sisters reaction. It wasn't technically a lie and the best lies always hold a shred of truth.

{Yes it makes sense now my sister claimed that his feeling for her but noting more then airs he put on out of fear of her magic. And he decided that proving that he did not fear death was the best way to rid her of that notion. I must make sure I follow their relationship closer. I started this with my careless question at breakfast and it was only because my sister stepped in that nopony got hurt. I must make sure this human doesn't strike out before I find a way to break his bond with my sister.} as Celestia thought this she spoke." I see so a lovers quarrel then? While I know that it is important in a relationship I would appreciate it if you don't bring innocent ponies into it in the future."-Celestia said teasingly as she looked at her sister

"We are not lovers sister. Night surely harbours no such interest towards us."- Luna said looking at the ground

As Night watched the exchange he reminded himself just how skilled Luna was in the art of deceit she had spoken the truth with her words. Yet used her body to tell the lie and convinced her sister into believing even stronger in his non-existent feelings for Luna. He thought of aiding her into furthering the lie but he decided against it not wanting to risk tearing down the spider web Luna had made in front of her sisters eyes with her lies.

"No I suppose you are not but if anything this incident shows that his affection for you is genuine does it not"-Celestia asked her sister as she looked at Night who instantly looked away not wanting to meet her gaze.

"We suppose thy are correct. We shall consider this but for now we have answered thy questions so answer ours as well. Who was this "Prince" of the house of Blood?"-Luna changed the topic. She needed to increase her supposed love with Night Shadow to deceive her sister but she did not wish to have to set aside time for this deceit just yet. She still had to catch up on what had happened in her absence and figure out who she could trust to aid her in dethroning her sister. Pretending to be in a relationship was something she would avoid as long as she could as it would be time consuming.

"I shall send meals to your room as I am sure you are both very tired from this whole ordeal. I am sure that you can lower my sun sister so I shall head for bed see you in the morning sister and I wish you sweet dreams."-Celestia said faster then what should be possible and then teleported away.

Author's Note

So glad I could save the challenge. After all the comments demanded Josh win.

Comment on anything and there can be still like 1-2 "weapon" suggestions if someone wants

No modern weapons thou Josh sort of comes from the past( fighting with swords and chains and the like) and equestrian isn't really technologically advanced for guns what with Celestia keeping any potentially dangerous new discovery under wraps to ensure that her ponies are safe.