Strong positive emotions:
* Passion: A strong and overwhelming feeling of love, excitement, or interest.
* Enthusiasm: A feeling of intense interest and excitement.
* Zeal: Great energy or enthusiasm in pursuit of a cause or an objective.
* Care: A feeling of concern, fondness, or affection.
* Interest: A feeling of wanting to learn more about something or someone.
Strong negative emotions:
* Apathy: A lack of interest, enthusiasm, or concern.
* Hatred: Intense dislike or aversion.
* Anger: A strong feeling of displeasure and hostility.
Other possibilities:
* Concern: A feeling of worry or interest.
* Attention: The act of focusing on something or someone.
* Engagement: The act of actively participating in something.
The best opposite for indifference will depend on what you are trying to express.