If you're looking for manga similar to Code:Breaker, you might like these titles. All recommendations are made by Anime-Planet users like you!
Samurai Deeper Kyo is a story of two men in one body - the humble, polite Mibu Kyoshiro and the legendary samurai Onime-no-Kyo, who has a price on his head. Consequently, Mibu Kyoshiro is captured for having an uncanny resemblance to the samurai. As the story of SDK progresses, we learn more about the two unique souls that inhabit the same body.
If you liked Samurai Deeper Kyo, you'll like Code Breaker and vice versa. Both being from the same mangak, you won't be surprised by the similarity in the design and the story telling. Both are about a young man at first looking like a dangerous person bearing an incredible power, but the main girl will be able to gradually change him and reveal that the main male isn't as bad as he seems to be. A lot of actions, awesome fights and great story telling.