Cannons (砲台) are artillery objects that uses gunpowder or other usually explosive-based propellants to launch a projectile. Various cannons exists in the Touhou Project, including Utsuho Reiuji's control rod.
Cannons appear on the first and Extra stage of Story of Eastern Wonderland as general enemies with a taijitu symbol on them. These cannons are likely created by Rika since she says that everything on stage 1 were created by her. They were officially referred to as "Cannons" (砲台) in the strategy guide. When Reimu Hakurei and Genjii get to the bridge of the stage, some cannons will pop out of the water on both sides of the bridge, shooting danmaku at them. They'll stop once the midboss Shrine Tank appears. If playing on lunatic, they'll shoot danmaku as return fire if destroyed. The cannons are a bit more vigourous with their danmaku on the Extra.
Utsuho Reiuji has a cannon attached to her arm, called a "control rod". This is because ZUN wanted to avoid giving her an actual third leg, basing it on her species Hell raven (Yatagarasu), so a cannon was used instead. With it, she's able to control the ultimate energy: nuclear fusion. She treats it as a typical cannon in Touhou Hisoutensoku.
The Five Magic Stones with their 24 laser cannons
- There's a logical mistake in the scripts when the Story of Eastern Wonderland cannons suppose to pop out of the water. At first appearance, they'll sometimes pop out of the ground next to the water and still show animation of water around the cannons. On the extra stage, there's no water shown, but they still show the appearance of coming out of water anyway.
- The Five Magic Stones are referred to as "Cannons" (砲台) in the Japanese fanbase due to their appearance of a battery cannon.
- Interview on Subterranean Animism with Cara☆Mel (Nico Nico Video link)