This item is also seen in the canon Corpse Party games. You can find it here.
The Loose Board (木の板,Ki no Ita?, lit. "Plank of Wood") or (ボロの板きれ Boro no Itakire, lit. "Rickety Plank") is an item that appears throughout many different Corpse Party fan games.
In CORPSE-PARTY-0, Kaori Hasegawa's party find a Loose Board (ボロの板きれ,Boro no Itakire?) inside the entranceway of the abandoned schoolhouse. They use it on the gap in the first floor hallway to the stairway leading up to the second floor.
In CORPSE-PARTY -Cross Fear-, Sayako Kasui and Seita Kanemoto find the Loose Board (木の板,Ki no Ita?) inside the principal's office on the third floor. They use it on the gap on the second floor's central hallway to gain access to Kaori's side of the schoolhouse.
In Corpse Party D2: Depths of Despair, Ayumi Shinozaki finds two Loose Boards inside the science lab while running away from Yoshiki Kishinuma in Chapter 2. She uses one right away inside the science lab and the other one in the second floor hallway. After that, the latter one breaks, saving Ayumi from Yoshiki's vengeful spirit.
Ayumi will find three more loose boards in classroom 1-B. She uses one to escape the room, another in the second floor hallway to replace the one that fell down, and the last one in the first floor.
In CORPSE-PARTY if, Yoshiki and Akari Minamino find the Loose Board (木の板,Ki no Ita?) inside classroom 2-3. They use it to gain access to a classroom located on the first floor.
In CORPSE-PARTY if PAST END, after speaking with Ayumi's corpse in the science lab, a Loose Board (木の板,Ki no Ita?) will appear. Yoshiki will grab it to use it at the 2F north hallway on the gap, allowing he and Akari access to a dead end on the first floor and to the third floor.