involvement as a party concerned; degree of involvement; relevance to oneself
Abstract noun often used in discussions of social issues, ethics, or personal responsibility. It refers to the quality or degree of being directly involved or affected, rather than a mere bystander. Common in phrases like 当事者性が高い (high degree of personal involvement) or 当事者性を感じる (feel a sense of personal stake).
This issue has a high degree of personal relevance to me, so I want to think about it seriously.
Through volunteer work, I felt a real sense of involvement in social issues.