In Tartarus (this was also way back before Y/N meet Thor or Beelzebub)

*This is the prison of the gods, where light can never shine. It was a war between the Giants and the Greek gods. But then the remaining titans were able to escape from Tartarus and join the Giants. they were able escape and caused panic in Helheim. However The Goddess of the Underworld Hades was going to stop them as she is right now,*

Hades:

Hades: Come on is that all you can do!*very damaged and is being overpowerd*

*The Titans are everywhere and Hades is having a hard time fighting them and it looked like she was loosing*

Hades: *Is this... how I die... Oh well... If I die protecting my sibling then it's worth it. But the problem is-* I won't give up!

*Hades then got even more serious and continued fighting lucky for her someone came*

Y/N: Hey is everything ok in here? *confused face also having a scabbard whit a sword*

*Everyone stoped and looked at Y/N Who was standing there not knowing what was going on*

Hades: Why did they stop? *sees at what they were looking at and was surprised* *What is a mortal doing here !? It's not safe!

Titan 1: What is mortal doing in Tartarus. Are you whit the gods.

Y/N: Ummmm no. I was just pacing by and saw a huge fight here so I came.

Titan 1: You're pretty calm for someone who is in Helhim and seeing a group of Titans.

Y/N: Oh I'm not worried! I can beat anybody here.

*Everyone except Hades started to laugh*

Titan 1: HAHAHAHAHA! THAT'S GOTTA BE THE BEST DAMN JOKE I HAVE HERED!

Y/N: Well believe it or not I can beat you.

Titan: Oh really then... *throws a punch at him really fast* SHOW ME WHAT YOU GOT!

Y/N: *he dodged his attack and Stops his punch as he broke his arm causing him to back away holding his arm as everyone was shocked*

Titan 1: W-what hell!?

Hades: *Shocked* *What was that... is he really mortal or something else?*

Y/N: I told you and you didn't listen.

*The titans that surrounded Y/N tried to attack him but instead of them hurting him*

*Y/n puled the sword out of his scabbard whit flames on the sword, Y/N then spined himself creating a vortex of fire and slashed the heads of the titans that tried to attack him*

The sword:

Titan 1: Everyone! Attack this mortal, he is a greater threat to us then Hades!

*Y/N then noticed hades and rushed towards her*

Y/N: Names Y/N, Y/N L/N! *He ten picked up bride style whit Hades blushing and rushed to higher ground*

Hades: Let go of me! If they get out my siblings will be in danger!*Tries to move but is to damaged*

Y/N:*Gets on higher ground and puts her down* You have to rest, I will deal with the Titans.

Hades: You!? If I couldn't beat them all then why do you think you can!? Plus I'm not letting you fight them all alone, you will die! Let me help!

Y/N:*smiles* You have done more than enough to protect you're family. Now rest, and heal.

Hades: *Blushed* W-While I appreciate the help I can't allow myself to rest until my duty is fulfilled. Until  then I will not re-*she fainted before she could finish her sentence*

Y/N: *Grabs her before she could fall and pus her down* Rest well, Hades Goddess of the Underworld.

 *he then went back down to fight the titans as, he was fast enough to catch whit the Titans*

Titan 1: Finally, you stop hiding like a coward and fight us like a warrior!

*Every titan then ran towards Y/N as Y/N then used his sword and made a huge fire slash whit his sword and killed every titan that tried to Titan but Titan 1 was on the edge of death*

Titan 1: Wha-what t-the Hell are you...eeeeeeeeeeee

Y/N: I am Zygarde the Defender of Order! And I will not let the world suffer.

*The Titan then died but Y/N wasn't happy of what he did, he only kills if it's necessary either if his life or the life of others are threatened, but he does feal remorse for people even if they did bad thing's or tried to kill him he would still feal bad for them, this was his first time killing someone since he never really wanted to*

Y/N: I'm not sorry for what I did, Titan's... but I am sorry I had to do it.

*He then grabbed there body's and made graves for them, after he was done he went back to Hades to help her recover*

At the Battlefield where the  Gods of Olympus and Giants were fighting

*After the long Battle the Gods of Olympus won the war*

Zeus:*he has a few scars but still happy* We won!

*The army of Olympus and the other Gods cheered whit happiness except for Poseidon, instead she has a blank look on her face*

Poseidon: Where is Hades?

*yet when she aske that question Hades army was sad and put there fists on their chest whit there heads down*

General: ...*small tears came*  L... Lady Hades... Wished to stop the invasion of Titans... and went to Helheim alone...

*Poseidon had a shocked expression on her face so she went to Helheim to find Hades*

In Helheim

*Y/N was sitting down on the floor recovering Hades wounds*

Hades: *starts to wake up* Ufff... Wha- What happened? *tries to get up but hurts to much*

Y/N: *Puts her back down as to not move* Hades please rest and save you're strength...

Hades: But what abou-

Y/N: Don't worry about the Titans I was able to defeat them.

Hades: *Shocked* You... killed them... alone...

Y/N: Please... don't use that word... I did do that... but I'm not a fan of killing.

Hades: *guilty* Oh... I'm so sorry.

Y/N: It's alright you didn't know... just rest. *sad*

Hades: *noticed his sadness because of killing* You're not a fan oof that (killing) huh?

Y/N: No... not at all. I only do it if it's necessary, or if my friends are in danger or someone very close to me. I would rather do things peacefully then kill.., that would be my last option and knowing Titans they wouldn't do things peacefully so I did what I had to.

Hades: That's very admirable of you. You would rather solve things peacefully then choose violence as an answer. And put others before you're self. You're a true definition of a God.

Y/N: *cute smile and surprise hugged her*

Hades: *surprised and blushed*

Y/N: Thank you very much Lady Hades, I appreciate what you said.

Hades:*smiles and hugs back* I should be the one saying thank you. If it weren't for you I would be dead. And you also healed my wounds. What is you're name?

*They stoped hugging*

Y/N: Y/N L/N.

Hades: Y/N, I the goddess of the Underworld am forever thank full for saving my life. If you're ever in trouble or if you pass away I will come and help you.

Y/N: Thank you very much Lady Hades.

Hades: it's just Hades. So friends? *gives a hand to hand shake*

Y/N: Friends. *both make a handshake and smile at eachother*

Hades: Oh I have to go back. You can come whit me if you want?

Y/N: Oh sure, as if it's ok whit you and you're siblings? *Smile*

Hades: Don't worry I'm sure they won't mind. *fake smile* *Except for Adamas and Poseidon they won't like because he's a mortal and yet he was able to defeat every Titan*

*Y/N noticed that he forgot to heal Hades right eye*

Y/N: OH! I forgot to heal you're right eye.

Hades: Wait, no that's ok you don't need to.

Y/N: Huh why not? You're eye is in a really bad shape. If you let it bee like that you're eye will lose it's eyesight.

Hades: I'm aware of that, but I am proud of having this scar, even if I failed it was a proof I tried to defend my home and siblings.

Y/N: *smiles* Say no more. *his hands start to glow green and were creating a specially-designed eyepatch (the same one from the manga and anime)* Here I made this eyepatch for you to be able to see. You're eye will still have it's scars but you will able to see. But you won't able to see whit out the eyepatch want's if it's destroyed or taken you're eyes.

Hades: *shocked* I-I don't what to say thank you Y/N. *smiles*

Time skip

*They then went and Hades lead the way to the exit of Helheim, as they were walking Hades asked Y/N something and stoped walking*

Hades: Hey Y/N?

Y/N: Yeah what is it?

Hades: I wanted to know more about you're sword that you used to ki- I mean defeat the Titans whit, If you don't mind asking, I'm just curious and also more about you?

Y/N: Go right ahead, ask me what ever you want. *cute smile*

Hades: *Blushed* Well my first question is how or where did you get that sword? This kind of weapon isn't common being whit mortals, only Gods can posses such weapon?

Y/N: Well I made it this sword.

Hades: I don't believe that.

Y/N: *Smiles* I didn't except you too. Well you see I have very unique powers and whit them I was able to create.

Hades: Can you show me this power you have?

Y/N: Of course.

Y/N:

                                                        (pretended that is Y/N in human form)

*Hades wasn't expecting this at all but then*

???:  Amhitrite!

*A barrage of a trident create afterimages directly hitting Y/N and pushed him far*

Hades: Poseidon!?

Poseidon:

Poseidon: You've been far to reckless Hades...

Y/N: *He got up, his green aura was around and was charging an attack*

*he attacked Poseidon whit great force and speed that as Poseidon wasn't expecting this and couldn't dodge the attack, after the smoke was gone Y/N was standing and had a serious face as Poseidon was still standing but she has many bruises*

Poseidon: You... will...PAY FOR THAT MORTAL! *Tried to move but was to damaged to* Urrrrrh....

Y/N: Hey sorry about that but you attacked me first.

Poseidon: You were going to hurt my sister! Of course I would attack you!

Y/N: What? Wait you're Hades sister that must make you Poseidon Goddess of the Sea.

Poseidon: Yes that's me and I will be the last person you will ever fight!

Y/N: Wait! Let's not fight!

Poseidon: Why Scared mortal?

Y/N: For you're safety yes and me Hades are friends. Stay down and let me heal you.

Poseidon: Yeah, right! You're just trying to fool me!

Hades: Poseidon that's enough!

*Both Y/N and Poseidon looked at Hades who was standing there worried for Y/N and Poseidon*

Hades: He's telling the truth. He wasn't going to attack me I asked him to show me his power. So stop threating him and let him help you.

Poseidon: .... Fine, but this doesn't make us friends.

Y/N: Alright. *comes closer to her and uses his healing power to heal Her as Hades smiled*

*Y/N held his hands out and green arura was starting to surround Poseidon body*

Poseidon:... Thank you mortal. *is not looking at Y/N*

Y/N: You're welcome. The names Y/N by the way.*smiles*

Hades: I take it you all have won the war dear sister.

Poseidon: Yes, however... *gets up and goes closer to Hades* You could have been defeated.

Hades: Well you're not wrong, if Y/N didn't show up I would have died.

Poseidon: *actually looks at Y/N* You defeated the Titans and saved Hades.

Y/N: Yeah. *cute smile*

Poseidon: *Blushed a little* Thank you Y/N. But you shouldn't do these kind of things alone Hades. You still could have been defeated...

Hades: That's because it will never happen again, especially in this moment.

*Poseidon was shocked to her what her sister said*

Hades: I see know that I wasn't able to defeat the Titans alone. I wasn't strong enough to defeat every titan and defend my family. So I will train till I become strong whit Y/N's help.

Y/N: My help, how can I help?

*Hades gets close to Y/N*

Hades: You were able to defeat the titans alone whit no help. I want you to train me for me to make me stronger. So that I can never lose and defend my family. So please let me be you're apprentice.

Y/N: Are you sure? It won't be easy at all and it will be long.

Hades: Yes. *confident smile*

Y/N: Well alright then. If it means that much to you I will train you. *smiles*

*Poseidon was in complete shock, she never thought that a mortal will train one of the strongest gods*

Hades: Poseidon...

*Poseidon looks at Hades*

Hades: When I become stronger, I swear that I will not lose to anyone. As the elder sister I shall not be defeated.

Poseidon:...

Hades: Perhaps you're right, I was far too reckless this time... But even still...

Poseidon: Hmph... *getting closer to Hades* You will not hear any thanks for me... *got close and hugged her sister whit a smile* sister.

*They stoped Hugging and were starting to walk as Y/N fallows them but Poseidon stoped walking and looked at Y/N*

Poseidon: Why are you following us, we didn't say you can come whit us?

Y/N: Oh, Hades invited me to come whit you and hang out whit you all. *smiles*

Hades: 

Hades: Oh... right sorry I forgot to tell you. I invited Y/N as a guest as a form of appreciate. He's also going to live whit us since it will be a lot easier for us to train. *Hehehehe please don't kill me Poseidon*

Poseidon: *serious look at Hades and looks at Y/N but whit a less serious look* Y/N me and Hades have something to talk about in private.

Y/N: I understand, I will go a few feet away and won't bother you. *whit a cheerful cute smile walks away*

Poseidon: *Blushed but also angry* *Why does that mortal look so cute...* *turn to Hades* Hades I am ok if you talked to a mortal. But to invite one in Olympus crosses the line! 

Hades: Listen I know you