Alternative Character Interpretation: The security guard was just doing her job. She may not have known what Eiichi was up to. She will kill Kiochi if he tries to barge past her earlier, however when you rape her eventually it's not like she ever killed you because you can't choose that option and then get to that point in the game without reloading.
Designated Villain: The security guard. If you don't try to barge past her she's just being a security guard. There's no proof she knows what your brother is doing upstairs or is in on anything bad.
Unintentionally Sympathetic: Again, the security guard. She acts like a jerk by not letting you through - but then of course she is a security guard and just doing her job.