One Step to Being Dark Lord is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

“It’s just… it’s no different than a villager A…” “There can’t be anything stronger than me in this world!” Yuri, the king of the sea, came to the land to find the strongest devil in the world. But… when I looked in the mirror, I saw a little boy…? As soon as she gained her leg, all her strength disappeared… And yet, her tearful journey begins, still aiming for the top spot in the world!