I just watched episode 102 of Fairy Tail and had a super idea for a new story, now mind you I would write it myself, however I'm pants at it, so I'm sending it to you. Now the idea:
When Natsu goes on his One Year training trip, what if the Spirit King transports him to the Bleach universe and tells him to become Yamamoto for 2 Thousand years in return for which he would be given Ryujin Jakka and training that we know Yamamoto has. After he dies as Yamamoto he will be sent back to Fiore in exactly 1 year. The story will start at Yamamoto's final battle with Yhwach for the first time in 2 thousand years he will fight with everything, having not used his Dragon Slayer Magic in all the time there. The fight will have to be epic, y'know full Bankai, him laughing fully, using evrything in his arsenal, showing every one what true power is, basically going out with the mightiest of BANG.
Now the points you'll have to follow:
1) Natsu returns with all his acquired power, i.e., Zanpakutou, Kido, Zanjutsu, Hakuda, Speed and most importantly Experience.
2) Natsu doesn't use his magic or blade unless strictly necessary, even then not his Shikai nor Bankai. After all we all know what happens when he finally does.
3) Happy is transformed into female, Yoruichi and she comes back with him with that power(Talking cat with power to transform into a super female).
4) Igneel is Ryujin Jakka.
5) Natsu keeps his new hairstyle.
6) Natsu wears Yamamoto's clothes and has his sword in cane, its makes for epic scenes.
7) Natsu only releases Shikai for Upper Level Spriggans and Bankai for only Zeref Level opponents. Natsu is OP. He uses his physical prowess and speed and simple hand to hand for normal mages, Fire Dragon Slayer for S-Class and finally Kido for Wizard Saints and up.
8) Natsu has learned manners and decorum but outside of serious situations he is carefree, free from very high responsibilities but he is very serious and strict in political, battle and other tense situations.
9) He also uses his reiatsu on opponents to intimidate them and on weak and arrogant opponents he uses the line,"Listen well, be gone from here... I have neither the time nor the patience to teach a mere infant like you how to breathe." in a cold tone. It's awesome.
10) Please use the real names for the Bleach techniques, you will find them in videos with English Sub in them, after all Ikkotsu and Sokkotsu has a different impact than Single Bone or Double Bone.
11) The pairing is NatsuxHarem(Erza, Kagura, Mira, Retsu). Natsu and Retsu are 23.
12) Retsu comes with them after ther Spirit King(Rei-o) saves her soul and reverts her age to 23. She joins Team Natsu as the medic. She no longer has her scar.
13) All three are not immortal. Natsu is not E.N.D. Zeref can be harmed by Zanpakutou(Soul Slayer). Only Natsu and Retsu have zanpakutou, nobody else, not even Happy/Yoruichi.
14) Natsu is either temporary Master or full Master but he will be one of The Four Gods Of Ishgar.
15) He visits Mavis' grave on Tenrou then meets Lucy in Crocus with Retsu and Happy.
The rest I leave to you. Though if you need help PM me. Also put some emotion in you dialogue delivery, add some exclamations and some question marks.
Thank You.