
Nagakiba can be upgraded by using Smithing Stones. This weapon can be infused with Ashes of War. This weapon comes equipped with the Piercing Fang Ash of War when obtained, which can be removed for its default skill. If killed by the Zamor Ruins site of grace, you can loot the Ronin Armor set from him and the weapon will be found in his usual spot just north of Murkwater Cave or it can be found south of the Dragon Burnt Ruins under the broken structure. on the edge of the bridge a little way away from the Main Academy Gate Site of Grace. at the underpass below the Murkwater Coast Site of Grace, or 3. at Yura's camp north-east of the Seaside Ruins Site of Grace, 2. If his questline is progressed too far without killing Eleonora (to the point where his body is taken by Shabriri), the Nagakiba can be found in one of the prior locations the player saw Yura: 1. Can also be obtained by completing Bloody Finger Hunter Yura's questline at the Second Church of Marika allowing you to also obtain Eleonora's Poleblade and Purifying Crystal Tear. Dropped by Bloody Finger Hunter Yura to the north of Murkwater Cave or in his camp near Seaside Ruins Site of Grace. The Nagakiba weapon can be found at the following location: Reminiscent of a reinforced spear, its imposing length can be put to good use with powerful thrusting attacks. There's a Biovida facility here with gunpowder inside one of its warehouses, it's also part of the mission Intervention.Signature weapon of Yura, hunter of Bloody Fingers. Take out this checkpoint to get some gunpowder. Clear the checkpoint out and there's some gunpowder in the office. There's gunpowder on the ground floor just inside the front door. There's a mansion here you'll attack during the Secure Marquessa Villa mission. The radio tower here has gunpowder at the very top (you visit this area during the mission Restore the Radio Network). There's a coastal checkpoint here with some gunpowder. You'll also visit here as part of the mission Room Service. There's a hotel here with some gunpowder in an office. You'll also visit as part of the mission to get Chicharron the roaster. You can find a monument here with some gunpowder in the square. There's a checkpoint here with gunpowder in the office. You'll find the Gran Roca Telecom Station on top of a mountain here with some gunpowder to take once you've cleared out the enemy. Along this road is another electrical substation you can break into to steal some gunpowder from a create. There's an Academy here you'll encounter during the missions Re-Education, with an FND crate containing gunpowder on the ground floor by the stairs. You'll also visit here as part of the mission Break the Chains. There's a prisoner camp here with some gunpowder you can loot from a crate. Another checkpoint you can take down and find gunpowder inside the building. There's a checkpoint here you can take out with gunpowder in the main office. The Castillo Senorial Tobacco Factory has a crate with gunpowder inside one of it's buildings. Look for a small electrical substation just off the main road here to find some gunpowder. You'll find gunpowder on the construction site near the blue and white building you enter as part of the Blood Ties mission. There's some gunpowder in the checkpoint here. There's some gunpowder between two of the blue and white tents during the Clear the Air mission where you have to destroy the poison tanks. You'll get some gunpowder as part of the second Chirozo mission, Fetch Quest, when you find him on Montero Farm.
There's gunpowder on the ground floor of the mansion you visit as part of the Meet the Monteros mission. There's some gunpowder on the bridge of one of the ships in the Quito Bay Blockade. You'll find some gunpowder during the Sabotage the Viviro Nueve Plantation mission, on the roof of the blue building with the Biovida signs. It's in a red FND crate in the same room as the Uranium. You'll find your first gunpowder in the fort during Juan's Du or Die mission. However, if you want to collect some gunpowder fast this definitely will help you get started quickly.
You might take a different route through Yara and the available missions.
It's not an exhaustive list, obviously - it's the result of our passage through the game in the first 30 or so hours. The map above contains 25 locations where we've found Far Cry 6 gunpowder in the world so far.