Sometimes all-katakana is used in fiction to indicate foreigner or robotic voices (like the Starmen in Mother 2). Writing a scream as a string of ア's instead of

Sometimes all-katakana is used in fiction to indicate foreigner or robotic voices (like the Starmen in Mother 2). Writing a scream as a string of ア's instead of あ's gives it a piercing quality, moreso when you add the dakuten marker (゛), even though it doesn't change the pronunciation in this case.