The song 相思創愛 (Soushisouai) is a key entry in the Kotonoha Project (言ノ葉Project), a narrative-driven song series composed and written by renowned pianist and NicoNico Douga creator marasy (まらしぃ). Released as Chapter 5, Part 1 of the project's first season, it forms a two-part story arc alongside its counterpart 天国と地獄 -言ノ葉リンネ-. The track brings together two prominent vocalists from the doujin music scene, Kashitaro Ito (伊東歌詞太郎) and Lon (ろん), whose contrasting voices weave through marasy's characteristically intricate piano-driven composition. The song's title combines the kanji 相 (mutual/reciprocal), 思 (longing/thought), 創 (creation), and 愛 (love), reflecting the Kotonoha Project's hallmark of layered, thematic wordplay. Marasy handled composition, lyrics, and co-arrangement alongside KOUICHI, while the music video was created by yama_ko with illustrations by Batiko. Lyrically, the song touches on themes of memory, unwanted power, distant happiness, and the tension between protecting bonds and embracing solitude, imagery that aligns with the project's overarching narrative. The full version appears on the album 言ノ葉カルマ - 言ノ葉Project ORIGINAL SOUND TRACK - 第一章. In maimai, 相思創愛 debuted with the MURASAKi PLUS update on August 24, 2017. It originally sat under the ORIGINAL & JOYPOLIS genre before being recategorized through subsequent versions. The Master chart, designed by ロシェ@ペンギン (Rocher@penguin), stands at level 13 with a notably high slide-note count of 126, while the Expert chart by LabiLabi offers an 11-level challenge. A VOCALOID version featuring Kagamine Rin and Len exists on marasy's channel, and the song later crossed over into CHUNITHM STAR and CHUNITHM SUPER STAR.