SWORD ART ONLINE: FATAL BULLET

This achievement unlocks after speaking to Kureha at the item shop to the right as you come out of your house when their affinity rank is at least 4.

You can check your current rank with any of the character by pushing cn_start then go across to the player icon and click on friend list, you can then push cn_X and down the bottom on the right, it will say their rank.

The fastest ways to gain points with the people in party is by reviving them.

On the Extreme difficulty, the snipers one shot everyone. Using the Photon swords skill Sword Barrier you can swoop in and revive them.

On the Normal difficulty the way I've been grinding this out is by fighting the Honeycombed enemy in Solitary Sand (Large mountain to the right of the map). This will require luck and being good at dodging.

The alternative solution is take on quests and go farming monsters. This will also help to level up your characters.

In order to unlock this achievement, you need to have Kureha at Affinity Level 4. The fastest way to raise affinity is by partying with Kureha and going out to fight enemies. Once she is Level 4, head to the shop in the SBC Glocken and talk to Kureha. This will activate a cutscene. You need to do this quite a few times but you'll get the achievement in the cutscene before this one.