This is a reference (I say this every year), to a hilarious-in-hindsight spam attack that was done on the old Castlevania Dungeons, many many moons ago.
A number of ne'er-do-wells gathered up on the night of 7|15 and initiated a large spam attack.
As a result, the mods at the time had to do some tidying up, as well as banning a few accounts.
Eric Roman was one of the co-conspirators, so he went to the banning box for a while.
He then proceeded to create an alternate account with those characters you see on the thread's first post, one being "Minoru", and later on being the maid. He infiltrated the forum (though most of us knew it was he, but did not have proof) and was non-combatant and communed well with the populace for a while.
Until he revealed himself and we were like 'OH SHOCK'...
...but honestly enough time had passed where he would've been unbanned anyway.
It was something like that.
Every year a little bit more of the details is further lost.
So now, we just have it as a little special in-joke in the Forums.
It's like our silly version of another 'terrorist attack' done in real life, hence the "7|15 nevar forget" (notice the vertical line between the 7 and the 15, and the oddly-spelled text afterwards).
We have matured since then. Now there's just some light trolling here and there, but nothing is warranting such levels of internet terrorism, here.