Kaikougata Jishin (a Touhou LW original) refers to subduction-zone earthquakes―earthquakes that occur in ocean trenches and troughs on the boundary between an oceanic plate and a continental one. This is the perfect temperament for this Koishi, who enjoys absolute freedom in this world of eternal summer. The laws of Phases and Essences have been cast aside, leaving a carefree optimism to enjoy the eternal summer and forget about everything else! "Summer is fun, so an eternal summer is always fun!" (Strong against Fire Phase.) "The beach is fun, so you'll always have fun if you go to the beach!" (Strong against Water Phase.) "The ocean is FREEDOM!" (Strong against Star Essence.) "What? I have to return home by a certain time? No way..." (Weak against Moon Essence.) The concept of opening and closing beaches for swimming can only exist in worlds that have distinct seasons. The beach is always open in the world of eternal summer, and this Koishi Komeiji is always having fun, so maybe her eye of love will open one day too.

The ability of Koishi Komeiji from the world of eternal summer (a Touhou LW original). This ability isn't all that different from the abilities of Koishis from other worlds. Unlike her sister, Satori, and their pets, Koishi was familiar with the surface even before the Underworld got flooded. She is so intent on finding and buying souvenirs because she wants to use them to decorate the entrance of the Palace of the Earth Spirits when they eventually return. Souvenirs are also called keepsakes or mementos and are intrinsically linked with memories, as shown in one of Satori's Spell Cards. They are a media that stores memory data. Perhaps Koishi collects them as a form of communication. Koishi is a satori youkai with a closed heart and mind, so no one can perceive her memories when they are sealed within her heart. That's why she records her memories somewhere else! Unlike keeping a diary or writing letters, she actually enjoys collecting souvenirs, so she probably won't give it up any time soon. Incidentally, it is said that fossils of shellfish can be found in the mountains. Some people used to wrongly assume that youkai could keep living in the flooded Underworld because youkai don't need to breathe to live. However, when the Underworld was flooded, it ceased being subterranean and became submerged, and the Palace of the Earth Spirits became the Palace of the Water Spirits. The hot springs also flowed into the ocean, and no one could eat the Hot Spring Town's delicious food anymore. The vengeful spirits would never stay in a place like that, and the oni also got sick of it. There was no other choice but to move to the surface and designate a specific area as part of the Underworld. This, of course, did not mean that the hated youkai were entirely free to live on the surface, as their past with the surface youkai couldn't just be ignored. It's easy to imagine that Koishi helped smoothen the negotiations because she often went to the surface to play before the flood. "I got lots of souvenirs again today! These are for Satori, these for Okuu, and these are for Orin!" Koishi cannot be remembered, so she wishes to leave memories behind. The souvenirs are the small roadside pebble's feelings of love. Summer evenings at the beach are like illusions, and the sea breeze slightly clears your dizzy head. The girl's feelings that cannot be recorded in history become fossils and leave their mark within the strata of the earth.