The Other category is a set of items that can be purchased in the Shop. So far, the Other tab only has Supply Cases that could be purchased with GP, and they have been added, removed, or replaced time after time.
In the early stages of the game, supply cases had contents that were pretty random from each other. The cases were a bit pricey, but had low rank requirements. Months later, category-specific cases have replaced all of the first few cases, making them easier to obtain a certain class of weapons, but had a higher Rank Restriction.