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stealth
travelling incognito (traveling)
ninjutsu
ninja
sneak theft; sneak thief
tolerance
忍びのような足音で近づいてきた。
He approached with steps as silent as a ninja's.
忍びの術を使って城内に潜入した。
He used ninja techniques to infiltrate the castle.
その間諜は忍びとして各地に潜伏しながら情報を集めた。
The spy gathered intelligence by hiding in various places as a covert agent.