2(Katekyo Hitman Reborn)

An Au where Tsunayoshi is Nana's child from a previous marriage(she lost her husband to cancer and then met Iemitsu who despite knowing she had been married and was pregnant, pursued her) and that changed how she acted.

Nana was very protective of Tsuna in fear that he may end up sick as her previous husband and she will lose him.

She loves Iemitsu but him being always away doesn't affect her much as most of her care and worries go to Tsuna so you can imagine how mad she was when suddenly her little ray of sunshine became so clumsy and empty after a visit of her husband and his boss.

The only reason why she didn't involve the police(as she assumed Timoteo had done some unsavoury things to her son and Iemitsu didn't stop him...because she hadn't known about flames) was because she first approached her previous husband's brother-in-law, Yamamoto Tsuyoshi(Tsuna looks the same as canon, Takeshi is a descendent from Asahi from his mother's side but someone from Asahi's main line married someone from Giotto's main line so both Takeshi and Tsuna still look similar to their ancestors...maybe Takeshi could have Giotto's blue eyes and Tsuna could have Asahi's eyes?), to know if she and Tsuna could stay with him as she didn't trust her son would be safe in the house Iemitsu had bought for them anymore.

Tsuyoshi, being an ex-hitman, immediately noticed the seal on Tsuna and knew he couldn't lie to Nana so he told her about the mafia and that the change in Tsuna was to blame on the seal someone put on him.

Nana's anger over what Iemitsu had been hiding and what he and Timoteo had done to her son woke up her lightning flames(maybe she could end up being Tsuna's lightning guardian until Lambo is older? I love Lambo but I would prefer he wasn't used as Tsuna's guardian in the beginning because he is still a kid...besides if Tsuna can have two mists why can't he also have two lightnings?).

These lead to Tsuyoshi training Nana in controlling her flames and find a good weapon for her(maybe daggers or a bow?) besides explaining about flames to their kids and start training them to defend themselves while they looked for a way to break the seal in Tsuna's flames.

Takeshi and Tsuna grew up as siblings and knowing about the mafia, no one messed with Tsuna both because of his protective mother and Takeshi as they hadn't been able to break the seal even if Tsuyoshi noticed that slowly the seal's strengths seemed to be deeming.

When Reborn appeared(let's say Iemitsu saw how similar Tsuna looked to Giotto and believed him to be his descendent while everyone else believed Tsuna to be Iemitsu's blood son), Tsuna despite his meek and clumsy personality wasn't going to just do as Reborn and Timoteo wanted so easily(he would only agree to Reborn's training as it seemed to be a way to try and break the seal).

Anything else is up to the writer including ships, how Tsuna not being Iemitsu's blood son may affect things, etc.