Talk:Shizune's route/@comment-68.83.123.161-20131124193830/@comment-66.62.136.142-20140504221625
From Katawa Shoujo Wiki
Also it was refereneced in Lilly's when Hisao realizes he's fucked Lilly twice without a condom but Lilly points to the birth control pills she's been taking.
And in Emi, they both did mention that they shouldn't make the stupid mistake of doing it without protection again (which led into why anal was a 'safe' experiment).