Osamake: Romcom Where The Childhood Friend Won't Lose
The Girl Who Lost Her Memories; The Octopus Wiener Trap
S1 E5:
Kuroha's younger sisters abruptly visit Sueharu's house to tell him that she has developed amnesia; all her memories from summer break onward are gone, and they stop right when she was about to confess to Sueharu.