ReZero Spoilers, the newest IF is kino
The most recent IF is called Tsugihagu.
In the main story, Subaru's memories are stolen by the Archbishop of Gluttony in a place called the Pleiades Watchtower. After waking up with no recollection of his circumstances, Subaru feels overwhelmed by the dangerous situation he's in, and suspicious of his allies. After learning about the Taygeta Library, where the memories of the dead are stored, he considers murdering his friends so that he can access their memories. In the main story, Subaru ultimately decides against this, but in Tsugihagu, he decides to go through with it. And so, with the assistance of Shaula--the Sage's apprentice--Subaru kills everyone at the Watchtower, and proceeds to hunt down everyone who knows the name "Natsuki Subaru," so that he can peice together all of the memories and become the "Natsuki Subaru" that everyone knows and loves.
Except, of course, it doesn't work.