In The Seven Deadly Sins anime, each titular Sin has a Sacred Treasure that allows them to fully harness their powers and abilities. The Sacred Treasures are each unique to their owner, having been gifted to the Deadly Sins when King Bartra Liones originally formed the group. Each one has a unique ability that its wielder can use to strengthen their own powers. Spirit Spear Chastiefol belongs to King, War Hammer Gideon to Diane, Twin Bow Herritt to Gowther, Demon Sword Lostvayne to Meliodas, Morning Star Aldan to Merlin, Divine Axe Rhitta to Escanor and Holy Staff Courechouse to Ban.
The last one to be revealed in the series is Ban's Courechouse. After having his weapon stolen, he is later reunited with it, bringing all seven warriors together once again. Here's what the Courechouse is and how Ban regains the weapon -- through slightly divisive means.
What Ban's Sacred Treasure Can Do
Courechouse is a staff that has four sections connected by chains. These chains can be lengthened to great distances and can maneuver at any angle, allowing the user to make large, sweeping attacks that span great distances. Ban can use it to unleash his full physical and mental strength to their maximum potential. Aesthetically, it is similar to the regular staff he uses throughout Seven Deadly Sins.
After the formation of the Seven Deadly Sins, Ban received his staff from King Liones. He used Courechouse constantly until he allowed himself to be captured by the Weird Fangs, at which point it was stolen from him. Along with Diane and Meliodas, all three Sins no longer had their Sacred Treasures by the time they met up with King, much to Ban's annoyance. It isn't until much later in the series that he's finally reunited with Courechouse.
How Ban Recovers Courechouse
During The Seven Deadly Sins' Demon King arc, a Demon Realm portal is opened, allowing for an Indura (a demon in its truest form) to invade Britannia. This Indura reproduces at an alarming rate, prompting Merlin to return Courechouse to Ban. It isn't clear when or how she found the weapon, just that she was in possession of it at that time. Ban is then able to use it to destroy nearly all the Indura offspring in one large attack.
The story behind Courechouse's journey since being stolen remains shrouded in mystery. It's never explained who stole it, but it could well be Merlin as she is the one who returns it to Ban. She also could've retrieved it sometime after one of the Weird Fangs stole it. The former explanation seems more plausible though, as it would be a very Merlin-like thing to do. Since she knew Ban was capable of escaping if he really wanted to, she figured his Sacred Treasure was safer with her until he needed it again. It's never clarified whether this is the case or not, but for now, Courechouse is safely back with its rightful owner in Ban.