Girls Logic Observatory performing live with several support mussicians at 新宿RUIDO K4 2018-02-03. From left to right: バツヲ (bass), 咲子 (vocals), うきね (vocals) テラ (guitar) & kent watari (drums). (twitter post)
Girls Logic Observatory are a Touhou arrangement circle who's music is primarily arranged and performed by sole member テラ who initially arranged primarily vocal Rock but has since branched out to include arrangement styles such as Jazz, Salsa and Pop. Vocals for the circle are notably contributed by both male and female vocalists, テラ himself sang on every album released by the circle up until the release of their third full album Reversible Negophilia in 2014. Releases by the circle regularly feature female vocalist 咲子 who is the circle's longest running recurring vocalists having debuted on the circles first mini album over knowledge in 2012, female vocalist うきね who debuted on the circle first full album Like a Retrospective in 2013 is another regular vocalist along with male vocalist 保科 who debuted on the circles fourth full album Hollow Masquerade in 2015. In addition to テラ and the circle's group of recurring support vocalists there are also a number of guest vocalists who contribute on full length albums, noteworthy past guests included ななせ of じゃねっと亭, イチ of 少年ヴィヴィッド and 556t of Kairo while as of 2016 vocalists あやぽんず* of ShinRa-Bansho and ななひら of Confetto have made regular appearances.
Nearly every album released by the circle notably features unlisted bonus tracks, these tracks most commonly include off vocal versions of the album's vocal tracks in addition to a commentary track narrated by テラ himself discussing the specific album's tracks or concept. All of the circle's discography has been neatly divided into either singles, mini albums, full albums or collaboration albums. singles and mini albums primarily feature vocals by the circle's group of regular vocalists and feature tracks that often end up being re-recorded for later full albums. Full albums released by the circle notably feature a number of guest vocalists both male and female in addition to the circle's regular cast of support vocalists and will often feature new material in addition to re-recordings/re-masters of tracks from earlier mini albums and singles. Collaboration albums released by the circle often feature new material by the involved circles, re-arrangements or covers by the circles of each others past works and new collaborative material.
A single featuring vocal and instrumental arrangements of themes from Embodiment of Scarlet Devil, Imperishable Night and more...?? The single features 2 re-recordings from the mini album over knowledge and 1 instrumental unique to the single.
A single featuring vocal arrangements of themes from Magical Astronomy and Dateless Bar "Old Adam". The single features 2 new arrangements and 2 alternate versions of previously released arrangements.
A single featuring vocal and instrumental arrangements of themes from Perfect Cherry Blossom and Subterranean Animism. The single features 2 new arrangements and 1 live recording.