Final Super Saiyan is the true last form for a Saiyan.
Final Sacrifice of a True Hero
After Krillin achieved Super Saiyan Infinity and was then beaten by Super Saiyan Z Goku it was thought Goku had finally achieved the last and final form of a Saiyan.
Unable to power down Goku decided he was to much of a risk to the entire universe. He feared his sheer power would crush everything out of exsistance. He also feared the power would corrupt him and thus make him evil like the power Krillin obtained did except this time no one would be able to stop the force Goku had become, knowing the powers of gods are to much power for one man to handle Goku knew what had to be done. He linked his mind to all beings in the universe so they would know of the sacrifice he would make with the hope it wouldn't be a vain. With this he gave his final message, he was going to do the ultimate sacrifice, he is going to destroy his very soul and being spreading his purity throughout the universes so with his last act he would diminish all evil so peace and good would have a chance to thrive and to make sure his power could never be used to hurt the ones he loves. Goku would never be able to be wished back or would he even exist anymore. With a final tearful good bye to close friends and family he activated his final move, Soul Destruction Kamehameha. In his final moments Goku had flashbacks of every fight he had ever had, every triumph he had and finally flashbacks of the good times he had with his family and friends, with the last one being the memory of all his friends and family together and happy. A blinding pure white flash burst outwards spreading throughout the universe.
Goku Jr was also seen transforming into this state when he saw no hope in winning the mighty omega z Shenron who powered up even more by absorbing the namekian dragon balls. Hoping that he would keep up a good fight he battled Shenron but Shenron proved no match for this legendary super saiyan form after barely surviving at the hands of Goku Jr, he suddenly reverted back into the super saiyan Z form. After proving no match for him he decided to ultimately sacrifice himself for the sake of humanity just like his great great grand father goku did.
Final Super SaiyanAfter the flash something surprising happened. Goku opened his eyes to find himself still alive, and what more he felt different. He knew he was no longer a Super Saiyan Z nor was he any other form of Super Saiyan before that. Goku had unwitingly achieved what was to become called the Final Super Saiyan. His power could no longer be sensed or felt anymore it was a power beyond any kind of logical measure. The sacrifice Goku was trying to make was the most purest and selfless sacrifice one could make, this is the final test for any pure Saiyan in the Super Saiyan Z form. Goku now was the Final Super Saiyan. This forms power being stronger than SSZ Goku at first feared it would adversely effect the universe but soon the knowledge came to him that this form was a pure form it could do no harm to others it made others stronger, healed the sick, gave a sense of calm and peace to all. Goku radiated pure good from himself now. The Final Super Saiyan also was hugely different from any other Super Saiyan form because the only changes it made to the physical apppearance to the user was bright blue eyes and a pure white tail, that was it. Goku returned to his family and friends a new pure being, with the added benefit that in this form he wouldn't destroy the universe but could also link himself to another in battle and have his power match theirs so he was at their level and truly equal in power. This way Goku could always compete in tournaments and could still spar with Vegeta without you know killing them by just looking at them. Peace would finally be had throughout the universe as the beacon of light Goku now was gave hope and peace to all.
After using the ultimate final explosion x10000000000, surprisingly like his great great grand father goku, he could survive by emitting pure white aura and by transforming into this ultimate form and there by two warriors goku and his great great grand son Goku Jr could only attain this form. Then after the epic fight all of his friends were revived but they couldnt sense his ki level.Then Goku approached him and said I am proud of you my grandson. Then onwards they lived on happily with their family and friends ever after.