Responses
Also for anyone else that is curious, the comment was found in the ending song of Toilet Bound (anime), I didn't watch the anime or even think about that until now, but I think in the ending song also give us the hint what will happen to Yashiro at the end...
I found this comment on YouTube by '@Haddy The Bored'. An interesting thing they said was that (in Anime) when Hanako gave the mermaid scale to Yashiro, he said it'll bind them in this life and the next life! Possible bittersweet, reincarnation ending? I went to go check the manga after this, in the 1st chapter they both swallowed the fish scale and their "fates have been tied together." "...They will be placed under a dreadful curse, but tied together by an extremely strong bond." Could it be their curse was to experience a tragic ending together, but meet again in their next life?