ってゐ！ ～えいえんてゐVer～ (Ttewi! ~Eien Tewi Ver~) is a Touhou Project arrangement by the long-running doujin music circle 石鹸屋 (Sekken-ya, literally "Soap Shop"), featured in maimai ORANGE PLUS since its release on March 19, 2015. The song takes its melody from シンデレラケージ ～ Kagome-Kagome (Cinderella Cage ~ Kagome-Kagome), the stage theme of Tewi Inaba from 東方永夜抄 (Touhou Eiyashou / Imperishable Night). Sekken-ya's arrangement transforms the original into an upbeat, energetic rock-pop track at 156 BPM, matching Tewi's mischievous, lucky-rabbit persona with a playful, hook-driven vocal delivery. The title itself is a pun: "ってゐ！" (Ttewi!) is a clipped, exclamatory rendering of てゐ (Tewi), as if calling out to the character, while "えいえんてゐVer" (Eien Tewi Ver) fuses her name with 永夜 (eien, "eternal night") from the source game's title. The song charted across all five standard difficulties, with the Re:Master chart, added over a year later on October 6, 2016, during the PiNK+ era, standing out as a particularly unusual design by はっぴー (Happy): a level 13 chart with zero hold notes and 187 slide notes, an extreme slide-centric layout that rewards precise, fluid hand movement over sustained holds. The MASTER chart by rioN and the Expert chart by Jack precede it in the difficulty curve, and the song's levels were rebalanced multiple times across maimai versions, reflecting its lasting presence in the arcade rotation across all regions.