Bou-eki Fuu (a Touhou LW original) refers to trade winds―winds that blow from East to West in the troposphere within a latitude of roughly -15° to +15°. It is the temperament of Eiki, who has long overseen the passage of souls between worlds as a member of the Spirit River Railroad. Eiki's temperament has undergone soul modulation at the fundamental level. Souls are hard to control, but the employees charged with their management at the Spirit River Railroad do not allow change (Moon Essence) or selfishness (Star Essence).

The ability of Shiki Eiki, Yamaxanadu from the Spirit River Railroad (a Touhou LW original). It is essentially unchanged from our version of Eiki's ability. However, given that the Spirit River Railroad is an organization unseen in other multiverses, it's predicted that some things about this Eiki, who has a strong connection to the Spirit River Railroad, are fundamentally different. Just like all parallel presences, even those from the same multiverse or universe may be influenced by their world's unique history. For that reason, any discrepancies between different worlds' Eikis have been stripped, leaving a description of her ability containing only its universal features. All raw data pertaining to the individual difference between Eikis is archived in a more secure document. This is the least that can be done out of respect for Shiki Eiki, Yamaxanadu, founder of Paradise and traffic controller for the Spirit River Railroad, a vast rail network of souls. The Spirit River Railroad is a giant system, almost like the combination of Higan, Yomi, the Netherworld, other worlds after death, the Ministry of Right and Wrong, and the samsara cycle, all of which exist in most universes. In other words, it's a combination of all things that exist in the space between the six realms (Heaven, the Human Realm, Hell, the Preta Realm, the Animal Realm, and the Asura Realm). Even though, strictly speaking, the Ministry of Right and Wrong and some official offices exist in Hell, they have been specifically excluded here. You can think of the Spirit River Railroad as the veins in a human body since they belong to no specific organ. Or transport facilities in a city. Or even as celestial bodies that travel between cosmic rays, interstellar matter, and solar systems. Why it takes the form of a railroad is unknown, but perhaps it has something to do with the fact it isn't simply arranged in a loop but in an intricate network of tracks. Due to increased management costs, swift and concrete reforms were introduced. Various areas of operation were mechanized and modernized... resulting in a railroad. This is clearly too big a change to have been completed by one world alone. The samsara cycle is a deeply traditional system that was established over a long period of time. Along the way, some sort of soul industrial revolution must've occurred. The track network of the Spirit River Railroad is so vast that not even Eiki has a full grasp of it. Perhaps one of the routes that takes you far away leads to whatever caused the soul industrial revolution. This world's Eiki's room is filled with her own personal clocks, known as her Proper Clocks, and she values all clocks highly. Of course, all of her clocks are exceptional magic items and could well be called "soul clocks." For her, collecting clocks is no mere hobby. They are important as they provide her with a method of viewing the proper time of infinite souls. Apparently, they are made of the same material as her Cleansed Crystal Mirror. This world's Eiki's whip, known as her Guiding Whip, is an important tool used to keep souls in order. The terminal station is as large as a major city and handles the transportation of incoming and outgoing souls. There, her whip functions as its own branch of government. She cracks her whip to guide souls to the righteous path. To do so, she utilizes sin. The whip originated from her Rod of Remorse, and striking a soul with it makes them momentarily conscious of their sins. In a similar way to neurological transmission, this causes them to move in a specific way. In other words, Eiki is able to herd souls like a shepherd would sheep. Universal Reincarnation is an ongoing area of research for Eiki. It is a form of reincarnation that, to some extent, takes place across the omniverse. Ultimately, the theory states that one person is everyone, and everyone is one person. Whether or not that's true has not yet been determined. At this point, it can only be said that there is no evidence proving this theory is false. However, this world's Eiki measures souls' proper time with her clocks. The reason for this can only be that she's considered the possibility that souls reincarnate freely into the past and future.