What?

Japanese warfare was ALL about sieges. Because of the sheer lack of any siege equipment, including catapults, battering rams, siege towers, or cannons, it was virtually impossible for a castle to be taken by brute force. As a result, the only way in was by siege. Similarly, a castle that was erected commanded an impressive amount of territory and influence: in fact Toyotomi Hideyoshi, one of the great "unifiers" of Japan, had as one of his "miracles" the construction of Sunomata castle overnight. While it is rather unlikely that the castle was in fact built in one night, it is likely that at least some sort of fortification was erected very quickly, thus giving his forces a substantial amount of control in, ironically, an upcoming siege.

Hideyoshi was probably also one of the greatest siegers himself. Following the Sunomata castle coup, he worked with his lord, Oda Nobunaga, on a plan to take out Inabayama castle. He sent in a small commando force through a small path to cause chaos and open the gates into the castle, upon which the main force was able to break in. In another instance, in the siege of Takamatsu castle, he diverted a river into a castle to flood it, and also constructed boats to act as mobile firing platforms for his arquebusiers during the siege. The only time where he was really foiled was at Odawara castle, which was said to be virtually impenetrable. Here, he instead just built siege lines to stop the enemy from getting in supplies or escaping and fed and entertained his troops until the defenders ran out of supplies.

This isn't to say that once a siege went up it never came down. Nobunaga tried to lay siege to the monk fortresses of Ishiyama and Nagashima on a few occasions. He failed to capture Nagashima two times before finally burning it to the ground on the third, and Ishiyama held out for four years before finally surrendering due to a political ploy (Nobunaga got the Emperor to issue a letter to the chief abbot urging his surrender).

So as you can see, plenty of sieges in Sengoku warfare. The advent of firearms did nothing to change that-if anything it made it even more important.