They are. Most ninja can seal things but very few, like me, specialize in them. It can seal more than weaponry though, so if you have a gun, or a grenade, or a ship or a bed or something you can seal it there. They can also be used to store -

[ She tosses the scroll into the air, which summons another larger scroll!

Yep. She really did just do that. The scroll lands comfortably in her hands with a huge smile. ]

A larger scroll!