Shin Honkaku Mahō Shōjo Risuka (Magical Girl Risuka)
Shin Honkaku Mahō Shōjo Risuka
Author: Nisio Isin
Artist: Kinu Nishimura
Volumes: LN 4 (completed), Manga 2 (ongoing)
Synopsis: The sociopathic elementary schooler unlike any other, Kugi Kizutaka—who is searching for "useful pawns" in order to achieve his own ambitions—comes to learn of Mizukura Risuka, a magician with the title "The Red Witch of Time." Risuka had left the Kingdom of Magic through the Gate, chasing after her father, a great mage called both "a God" and "a Demon." An unpredictable and unchained magical tale!
This one is sort of a contentious pick. Obviously Nisio Isin is a strong pull, but most of his other LNs have either been licensed by Kodansha (Monogatari, PBDC, Zaregoto, etc etc) or Viz (Zodiac War). Compounding this is that not only is the series complete, but it initially was published as a short story by Del Rey.
Still, if you're looking for older LNs to try out, or manga currently running based on them, it might be interesting.