Ever notice the coloured face on the List of Partner Characters and in the Client Order list?
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This shows how friendly a character is towards you. You can improve your relationship with a character by bringing them along in missions with you and/or completing their client orders. Increasing friendliness opens up new client orders and you can also get rewards from partner characters if you keep running missions with them.
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After a few missions with a character, they will have an item for you if you talk to them. You can also get rewards from the Title Counter for doing 10 & 100 missions with each partner character.
Most of the time these will be synthesisers, but you can get PA Discs that are rare or impossible to find in the field. Echo will give you :fire:Shifta and :light:Anti, while Maru will give you :light:Grants and :light:Gi.Grants.