From Koutetsu no Shoujo-tachi/鋼鉄の少女たち, taken from this tweet: https://twitter.com/wcqmb578/status/1462151331104231426
some military people force a boy to rape his girlfriend and then execute them both
the chapter is 16, but the series was axed before volume 5 could be compiled
the four published ones (up to ch14) are officially available for free on https://www.mangaz.com/series/detail/124641 but im not sure if theres guro scenes in them