Just drop the "memstick" folder into your main PPSSPP folder.

If you're using another mod for this game already (such as HD cards), do NOT overwrite the textures.ini when asked.

Instead, open your pre-existing mod's textures.ini file with a text editing program like Notepad or Microsoft Word or some such
then copy and paste the following line text in it somewhere:

000000008f9daa4f51d41b7c = characters/aki_izayoi/aki_body.png