For the uninitiated, "Desu" (です) is a Japanese copula often associated with the "kawaii" culture of anime. In the West, it became a meme thanks to Higurashi: When They Cry and the general otaku culture of the early 2010s. So, a site named "DesuArchive" immediately signals its target audience: anime fans and board culture veterans.
This is where it gets niche. Many prolific (or infamous) anonymous posters use tripcodes (a cryptographic signature). DesuArchive allows you to search for every post made by a specific tripcode. It turns anonymous posting into a pseudo-identity, allowing researchers to track "legacy posters" over years. desuarchive