Drill Shoujo Yui

In the early 21st century, remnants of a WWII research team orchestrated devastating terrorist attacks. An international special unit put an end to their activities. A decade later, the protagonist, a retired member of that unit, travels across Japan. A woman approaches him, proposing a new unit to track emerging threats. He declines, until meeting a candidate—a young woman who lost family in that attack ten years ago. His life as an instructor begins.