[dragon1412]

Originally Posted by aohige

At first it's minor blank in your memory like... "wait, what was the name of that cute girl in my 3rd grade year? and where exactly was that plastic model store I used to go?"

Just finished reading. Wow. WOOOOWWW.
The Anime OP actually has something that the novel just now covered.
I guess the author input the anime staff.

Spoiler:

When you die, you go to the moon.
The moon is the Elder Tales "Test Server", which consists of underground dungeon.
No one has ever seen the surface world... till now. When you die, you get teleported to the surface of the test server, until you are resurrected. This is also where you lose piece of the memory.

Since Shiroe and the Silver Sword guild got wiped in the raid, because the raid bosses ignored the game rules and came to help a boss being raided, the SS group are devastated as that would mean end of raiding all together. Shiroe is devising a plan though... and leave it up to the Scheming Four-eyes to come up with a sisnister plan!

beaten to the punch well, it's just like aohige said, but to be more precise, at first no one questioned it since that just something simple like "what was my 1st model", " where was my manga again" just a little memories amiss, but eventually the Gap got widened to the point of forgetting things like everyday life, and this happened to many people, thus making people realized that's something is wrong.