The muddy older sister is unconscious and unable to distinguish between reality and dreams. - A younger brother who repeatedly plays obscene pranks on such an older sister. - As a result, it escalates into forbidden incest. - An older sister who resolutely tries to act like a ``big sister'', an older sister who becomes an outlet for her younger brother's sexual desires while she is almost unconscious from the mud, and an older sister who gets drunk and horny and has sex with her younger brother under the influence of alcohol.