If you're looking for manga similar to Brynhildr in the Darkness: The Moment (Light Novel), you might like these titles.
Widely known as "The Modern-Day Sherlock Holmes", Shinichi Kudo is doing amazing work as a high school detective. One day, he heads to an amusement park with his childhood friend, Ran Mouri. But there he spots two suspicious men in black, and sensing a case abrewing, decides to tail them. Unfortunately, one of the men quickly realizes that Shinichi is following them, knocks him out, and forces him to take poison. And when he comes to, he finds that his body has shrunk back to that of a child?! Starting that day, he took the name "Conan Edogawa" in order to not reveal his true identity even to Ran, and began solving cases as a little elementary school detective!
In the future, an organization called the GGP has taken control of the world. Rin Ogata was a promising up-and-coming ballet dancer, but suffered a serious injury while dancing and decided to quit. Years later in college, she comes across a club building and soon finds herself intrigued by a transforming motorcycle-like robotic vehicle called a "Rideback". She soon finds that her unique ballet skills with balance and finesse make her a born natural on a Rideback. However, those same skills also get her into serious trouble with the government.