Using a disassembled fuse and its terminals I guess I would rig an amp meter across that fuse location and see what kind of current draw you are looking at. A dirty high resistance connection somewhere or perhaps a bad cell in the battery could cause the issue. Have you had the battery tested? Have you pulled and looked at the other fuse terminals. Do you ride in the rain very often which could lead to corrosion. A good inspection of cables and connections would be the order of the day. Also, by the looks of the fuse, it has been undergoing some heat stress for some time before it blew.
Most of my bikes lights and any accessories are now on my Amplink, removing a lot of current draw through the fuse as well the ignition switch.
