The term 'NINJA'S ASSET' can be summarized as the crossword solution STEALTH, which is a 7 letter word. STEALTH is an important asset for ninjas, as it allows them to remain undetected while they carry out their missions. It is also a key element of ninjas' martial arts training, as it enables them to move silently and quickly without being seen or heard. Ninjas use STEALTH to gain an advantage over their opponents, allowing them to surprise and outwit them.