a special talent or skill that one is good at / an act or expression that one often does

first storm of spring

A group of onmitsu, government-employed undercover agents, established by the 8th Tokugawa shogun, Tokugawa Yoshimune (1684–1751). Sometimes described as ninja.

deathwatch beetle

(2channel slang) repeating something for the n-th time

an International Standard Book Number