adverb, adverb taking the 'to' particle, taru-adjective
suddenly; all of a sudden; unexpectedly
Formal or literary adverb describing an abrupt, unforeseen occurrence. Often used with として or directly before a verb.
Suddenly, the sky grew dark.
He disappeared unexpectedly.
All of a sudden, it began raining heavily.
A large earthquake suddenly struck.
One day, he suddenly vanished without a trace.