Positive affinity will reveal some of the companion's background and how they ended up here.

Raising or dropping a companion's affinity to a certain amount will trigger a unique dialogue with the player character.

These comments can be hateful, disdainful, neutral, admirable, generous, and for romantic companions, affectionate. They will also differ in attitude when dismissing them or asking them to join.

Companions will give different thoughts and relationship statuses depending on their relationship with the player character.

Hancock and MacCready will do the same if the listed crimes are done in Goodneighbor. For example, Piper and Nick will turn hostile if a DC guard/civilian is assaulted/killed, or if you trespass or steal.

Depending on where a crime is committed, the companion may even become hostile towards the player character.

Dogmeat, Ada, and automatrons are neutral about murder. This applies to every companion except Strong, as he likes murder. Should the player character ignore this warning and repeat a murder, companions will permanently leave. They will refuse to speak to the player character at first, but after a few days, the companion will be able to travel again. They may also leave the player character instead of speaking to them.

If the player character murders an innocent, their affinity with their current companion will drop by 10% and will trigger dialogue with the player character expressing anger and warning them to never do it again.

If the Sole Survivor fires a weapon in a settlement, any companions present in that settlement will often become annoyed and make backbiting comments on how that is best saved for another time.

Piper, Cait, Preston, Macready, Old Longfellow and Porter Gage though being human are naturally immune to radiation but they will still take radiation damage from a gamma gun and radium rifle when used by enemies.

Some companions lose their essential status upon reaching the lowest level of affinity and leaving the player character.

They do, however, remain protected like other settlers and cannot be killed by NPC attacks (only by the player or their active companion or related action)

Some companions lose their essential status when dismissed.

If they're not healed within a set period of time, or when the player travels beyond a certain distance, they will leave and return to their last used home base.

If one is playing in Survival mode, the companion must be healed when incapacitated, even after combat.

If incapacitated, they will automatically heal after combat ends.

Unlike Fallout 3, companions are marked as 'essential' when acting as active companions, meaning they cannot be killed.

The game has a number of temporary companions that will only be available during certain quests. Steal Owned Items (may upgrade to Hack or Lockpick)

Fallout 4 companion face mod