How to start a short story with a flashback?

A story about a guy who gets 3 wishes and reincarnates in Legend of Korra as an earthbender prodigy. I always wanted to write fanfiction and the idea for this story kept popping up in my head so here we are. My main goal right now is to upload a chapter at least once a week and that becomes a lot harder when English isn't my first language. Besides that please be gentle with me as actually posting this took a lot of courage for me. I own nothing besides the OC.

WARNING my stories generally lack spirit i write for fun and to free my head from this particular plot. Expect inconsistency bullshit power ups and messed up logic and also don't expect good grammar.

Mc has a system in naruto and a few cheats from other animes

When a woman dies in the ocean with regret and hate, she becomes a siren to mesmerize men to sink their ships. When a woman dies in the snow in despair, she becomes a yuki-onna to freeze anyone who has the guts to look at her. When a raped woman dies with the desire for revenge in her heart, she becomes a succubus to suffer men and to be fed from them. This is my story; written for those who take the hard way instead of accepting death and rely on angels to bring justice. *Mature content *No underage character *No incest *No love, just lust

The most important thing for a qualified killer was amazing killing skills! However, Shi Yu was an exception. He was a killer, but he couldn't even hold a gun steadily. He couldn't even fight. That's right. He was not a qualified killer. You could say that he was a failure of a killer! Shi Yu was dejected and felt that not even God wanted him to be a killer. However, he decided to carry on to finish his father's wishes. Then one day, he got hold of a wristwatch and everything changed! "Ding! The Divine Weapon System has been activated..." "Selecting your first weapon..." "Ding! Selection Success! Your first weapon- poker cards!" "Ding! Congratulations, you are now skilled at poker cards. You can now make them fly!" The first task he received after receiving this skill had surprised Shi Yu. The ordinary poker card managed to cut the surveillance fly buzzing around in the air into two. This was a fly camera that was as nimble as a real fly! The doors to a new world opened before Shi Yu. This was the first time he realized that poker cards could be so dangerous!