In which mc, a failed soldier, did something wrong and so, is forced to go to the frontlines. One day, he is transporting a civilian somewhere, and they get attacked. Although weak, he attempts to protect her, but finds out that the "civilian" is actually a princess known for fighting with a large sword. When the attackers are defeated, the princess offers mc the position of strategist/tactician for the army.
At first, I thought it was hella slow. However, it gets better and better. A total must read. (I also have a guilty pleasure of strong girls and weak, but smart, boys. Ehehehehe...)
Haken No Kouki Altina (novel)