This Gunbuddy is a part of the battle pass Reflection: Act 1 that costs 1000 valorant points. The K/TAC weapon buddy is unlocked at level 2 of the premium battle pass.
Gunbuddies are charms that you can attach to any of your guns in Valorant. They usually come in pair of 2 so you can have them active in two different weapons at the same time. It’s also possible detach them and move to different guns.