Hey! There are two, kind’ve three ways: (1) if you choose to help your father on the farm as your activity and avoid the option of giving your allowance away to the bully, you’ll have the money to buy it. (2) you can steal it if you sneak into festivals as your activity or (3) if you first fail in your attempt to steal it, but then have deception of 65 or higher, you can still manage to trick the merchant and get it.
Affinity is unlocked with a mix of personality and stats. Personality: Charming (fire), diplomatic (water), reserved (air), broody (force). Stats: emotion (fire)/control (force), honest (water)/deception (air), wicked (dark)/virtuous (light).
Personality unlocks an affinity automatically and stats unlock them with a value of 60. I hope this helps! Let me know if you need me to go into more detail.