The user seals away the target's memories by burying an extremely small needle into the brain's memory centre. The memories can be restored by cancelling the technique, thereby destroying the needle. If a subordinate had this operation done on their brains and has infiltrated in enemy camp, they can safely perform spy activity over a long period of time with no memory of the procedure having been performed. If the user cancels the technique, the target will once again remember their mission as a sleeper agent.
Sennō, when written as '洗脳', means 'brainwashing'. The first kanji means wash and the second means brain or memory. In this technique's name, the first kanji has been replaced with the kanji for "conceal" or "hide" emphasising the fact this technique doesn't actually wipe one's memories, but merely conceals them.