A Parallel Sky
Sawada Tsunayoshi, a boy with a grave destiny, has always smiled. He will continue to smile, for the sake of his friends and family. Because a sky is meant to be reassuring, and accepting of all. And when he meets a young woman named Aria, the Sky Arcobaleno, and she tells him that he will be her successor. Tsuna had always been neglected by his family, since his older brother, Giotto, had moved away several years ago, and his mom had thrown Tsuna out as soon as he hit middle school, saying she doesn't have the money to pay for him to live with her. Aria introduces Tsuna to her 'friends' who are the other Arcobaleno's. And Tsuna disappears from the world, and is known only as the Sky Apprentice 27.
Tsuna has gained a new enemy, after ten years of peace and quiet. A powerful foe that not even Checker Face had seen coming. This new enemy has a plan, to destroy Tsuna, mentally and physically. And the start of his plan you say? Get everyone to leave Tsuna, since Tsuna's only fear, is having his friends and family leave him. Our new foe attacks Namimori knowing that the Vongola won't be able to stop him, since they were in Italy. The Guardians find out that all their family, and town, was completely destroyed, no trace of life anywhere. They all go into a state of depression, except Tsuna, and they start to ignore him, turning to hating him even, since if they never would have involved themselves with their 'heartless' boss, then their family would be alive and safe. Reborn and the other Arcobaleno have reverted to their original bodies and ages, and all side with the Guardian's, surprisingly, and Tsuna is hated. The foe ends up appearing before the Vongola, as well as the Varia, who have sided with their Tsuna in the matter, and Arcobaleno while they were in a heated meeting. And A secret gets out, and Tsuna's ultimate plan is revealed.