I play decree of focus in a showdown against a body and fury unit. Opponent plays thrill of the hunt and targets the fury unit and places it on another battlefield. Will my unit get +4 might?

No, your unit will not get +4 Might.

Sequence of Events

1. Play: You play Decree of Focus targeting a friendly unit at a battlefield occupied by an enemy Fury unit. It is placed on the chain.
2. Reaction: Your opponent plays Thrill of the Hunt in response, targeting their Fury unit. It is placed on the chain on top of your Decree of Focus.
3. Resolution – Thrill of the Hunt: Thrill of the Hunt resolves first. It banishes the target Fury unit, and then its owner plays it to a different battlefield.
4. Object Change: According to Rule 705 and RiftJudge FAQ #9870, when a unit is banished and then re-played, it enters the board as a "new object."
5. Resolution – Decree of Focus: Now it is time for your Decree of Focus to resolve.
   • The requirement for Decree of Focus is that your unit must be "in combat with an enemy Fury unit" or "being chosen by an enemy Fury spell."
   • Because the Fury unit moved to a new battlefield, the specific Fury unit that justified your targeting of the Decree of Focus is no longer present at your battlefield.
   • Per the rules governing mistargeting and condition checks (Rule 359.3.e), because the conditions of the spell are no longer satisfied, the effect fails to apply.

Summary: Since the Fury unit left your battlefield, your unit is no longer in combat with a Fury unit, and the Decree of Focus fails to provide the +4 Might.

Note: I could not fully verify this ruling against the retrieved rules.