Locate a friend in the Commonwealth, explore with them while making quest decisions and significant dialogue choices, complete small events to increase their affinity with you, engage in conversations with them, and (optionally, depending on the companion) complete their associated quest, and you receive a unique perk from each of them (except Dogmeat).
Berserk
Requirements: Gain maximum affinity with Strong
Thanks to your relationship with Strong, when you fall below 25 percent Health, you deal +20 percent more melee weapon damage.
Cloak & Dagger
Requirements: Gain maximum affinity with Deacon
Thanks to your relationship with Deacon, you receive +40 percent Stealth Boy duration and deal +20 percent more sneak attack damage.
Close to Metal
Requirements: Gain maximum affinity with Nick Valentine and complete Side Quest (Companion): Long Time Coming
Thanks to your relationship with Nick Valentine, you get one extra guess and 50 percent faster terminal cooldown when hacking.
Combat Medic
Requirements: Gain maximum affinity with Curie and complete Side Quest (Companion): Emergent Behavior
Thanks to your relationship with Curie, once per day you heal 100 Hit Points if your Health falls below 10 percent.
Gift of Gab
Requirements: Gain maximum affinity with Piper
Thanks to your relationship with Piper, you receive double XP for speech challenges and discovering new locations.
Requirements: Gain maximum affinity with Hancock
Thanks to your relationship with Hancock, at 250 rads or higher you get criticals 20 percent faster.
Hunter's Wisdom (* New perk from Far Harbor DLC)
Requirements: Gain maximum affinity with Old Longfellow, and complete Side Quest (Companion): Shipbreaker.
Thanks to your relationship with Old Longfellow, the Damage Resistance and Energy Resistance of animals and sea creatures is reduced by 25%.
Killshot
Requirements: Gain maximum affinity with MacCready, and complete Side Quest (Companion): Long Road Ahead
Thanks to your relationship with MacCready, headshot accuracy in V.A.T.S. is increased by 20 percent.
Know Your Enemy
Requirements: Gain maximum affinity with Paladin Danse
Thanks to your relationship with Danse, you deal +20 percent more damage against Feral Ghouls, Super Mutants, and synths.
Robot Sympathy
Requirements: Gain maximum affinity with Codsworth
Thanks to your relationship with Codsworth, you receive +10 Damage Resistance against robot energy weapons.
Shield Harmonics
Requirements: Gain maximum affinity with X6-88
Thanks to your relationship with X6-88, you receive +20 Energy Resistance.
Trigger Rush
Requirements: Gain maximum affinity with Cait, and complete Side Quest (Companion): Benign Intervention
Thanks to your relationship with Cait, Action Points regenerate faster if your Health is below 25 percent.
United We Stand
Requirements: Gain maximum affinity with Preston Garvey
Thanks to your relationship with Preston, you deal +20 percent more damage and gain +20 Damage Resistance when facing three or more opponents.