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Blood-Vessel Yin-Yang Orbs (血脈陰陽玉 Kechimyaku onmyō-dama) are a type of Yin-Yang, appearing as stage enemies on stage 3 and the extra stage of the PC-98 game Story of Eastern Wonderland. There are two types, a grey one and a red one. Grey ones come flying onto the screen in queues, sometimes from above, sometimes below Reimu Hakurei. On Easy, they'll shoot bullets directly at Reimu when they turn a different direction, but on Normal, Hard and Lunatic, they'll shoot those bullet as soon as they appear on the screen. On Hard, they'll shoot twice as many bullets, and if defeated on Lunatic, they'll throw bullets directly at Reimu as return fire. On the Extra stage, they'll create walls for Reimu to avoid, but later will quickly appear on the screen and shoot a circle of bullets. It takes a matter of a few shots to defeat them, but aren't trivial to deal with. It's unknown what their real names are or if they were created by Rika due to their extra stage appearance.
Red ones are a bit different, however. No bullet can defeat these, not even a bomb. The only way to kill one is to fly into one, thus losing a life. Luckily, they don't shoot bullets, and are made as an obstacle for Reimu and Genjii to avoid. Before the Five Magic Stones boss, they're combined with puffballs.
The name "Blood-Vessel Yin-Yang Orbs" is uncommonly used in the Japanese fan-base; it's named as such because of their tubular appearance like they're veins, especially with the red types. They appear very similar to the Yin-Yang Orbs Reimu possesses, as well as SinGyoku's first form and the flying yin-yangs.