As Kihara Enshuu charged forward in attack, the helmeted man calmly reached for the buttons of his coat.
Inside was…
“A convex shaped charge landmine!?”
“This is what it means to be a Kihara.”
He unhesitatingly detonated it.

A shaped charge landmine was a landmine created such that the blast went in a certain direction. If you wanted to punch a hole in the armor of a tank or other armored weapon, you could attach explosives to a crater-like concave sheet which would focus the explosive power in a single direction. If instead you wanted to spread the explosive blast over a wide area, you could attach the explosives to a mountain-like convex sheet which would spread the blast out in a fan shape. That kind was primarily used for anti-personnel mines that had to take out as many people at once as possible and they often had many small metal balls stuffed inside.

The helmeted man had held a convex shaped charge landmine under his coat.
Five hundred balls were scattered in a fan-shaped blast with a range of three hundred meters and an overall width of two hundred meters.

[...]

Shaped charged were made so the destructive force was aimed in a certain direction. In other words, in the other direction, one would not be harmed by the explosive. However, everything had a limit. If you were holding the mine when it detonated, there was no way you would escape unscathed.

[...]

“…Damn, she got away,” muttered the helmeted man.
The edges of his coat had been blown away. As if to explain his survival, a bent metal sheet fell from his chest, but that was of course nowhere near enough to protect him from a blast of that magnitude.

Toaru Majutsu no Index New Testament vol.4 main.12