I can work around currently untold backstories and vaguely implied plot events: with Kasen I have enough of an idea where its fine to leave that blank or I can just fill in the blanks with sensible head canon.
Fortunately I have a feeling they will be brought up eventually, especially with the current progression speed of the story, (Oh God I hope Kore Yamazaki doesn't pull a Zun.), but its still super frustrating.