介入
かいにゅう · kainyuu · JLPT N1 · noun
intervention
入 — single pictograph, two slanting strokes
入 is a pictograph showing an arrowhead or pointed entrance, with two strokes converging downward to suggest something going inward. The original sense was 'to enter,' and it still carries that meaning today. It contrasts visually with 人 (person), where the strokes cross differently at the top.