KanjiJLPT N1
Attack

attack, advance on, succeed to, pile, heap

Mnemonic

A dragon wraps itself in a stolen garment, disguising its massive form as a wandering monk. Villagers welcome it inside the gates. At midnight, the garment tears apart as scales burst through—the dragon unleashes a merciless attack, swooping through the streets with fire and fury.
Additional thoughts
Picture the garment as a cloak draped over enormous wings. The disguise is what makes the attack a surprise—dragon hidden in cloth until the moment of strike. The fabric shredding is the key visual trigger.
Quick recall
A dragon in a garment disguise sneaks past the gates to launch a devastating surprise attack.

Details

The keyword for 襲 is attack. This kanji conveys the idea of a sudden, often surprise assault or raid upon someone or something. It carries the sense of swooping down on a target without warning, as in a military ambush or a natural disaster striking an area. Beyond physical aggression, it can also mean to succeed or inherit, as in carrying on a tradition or title, suggesting something that "comes upon" one from the past.
On'yomi
しゅう
Kun'yomi
おそ.う、かさ.ね