Silent Earthquake (a Touhou LW original) refers to slow earthquakes where the slip between tectonic plates is slower than usual. This is an apt temperament for Koishi, who always appears out of nowhere. The Underworld youkai, who have cut off all communication with the surface, lack the three Essences of Sun, Moon, and Star. Koishi is endowed with Fire Phase, as she seems to have an out-going personality, and Water Phase, the element of the unconscious mind. The formless and passionate Fire Phase resists Wood Phase, because wood feeds fire, but it is weak to Water Phase, because water dampens fire. The flexible and patient Water Phase resists Metal Phase, because metal collects water, but it is weak to Earth Phase, because earth directs water.

The ability of Koishi Komeiji from the world of restless Underworld vengeful spirits (a Touhou LW original). It is essentially the same as our version of Koishi's ability. In this world, the disturbance where vengeful spirits burst out to the surface through a geyser has been prolonged. However, it is not clear whether this Koishi was part of the cause or not. There are many mysteries regarding Koishi's ability, but as the name of the ability indicates, there is no doubt that she can interfere with the unconscious mind of herself and others. Koishi's presence cannot be sensed with the usual five senses, so no one can notice her unless Koishi allows it or they have some other special means. Also, there is a high chance that Koishi's actions that don't seem to come from unconscious instincts are merely an illusion of conscious expression. Koishi's presence that is steeped in subterfuge and deceit is a continual threat to beings who have an ordinary mental psyche with both a conscious and unconscious mind. Koishi seems to only follow her playful instincts, but who knows if that is true... The Koishi of our world happened to meet Reimu and Marisa at Moriya Shrine after the disturbance calmed down. She appeared there without any plan of note because she was curious and wanted to give the powers of gods to her pets. However, the disturbance in this world has been prolonged and is still going on. What actions did this Koishi take during this disturbance, and what did she achieve? Perhaps those who encountered her could offer some insight.