円

Outer 冂 is the open-frame radical (Kangxi #13), two strokes forming a downward bracket and the indexing radical here. It wraps the character on three sides, picturing the rim of a round coin or coin-shape; 円 is the Japanese-style simplification of 圓 'round / yuan,' so the frame represents the circular outline.

Inner 丄 is an old variant of 上 'above', a small T-shape sitting inside the frame and serving here as the inner mark of a coin or roundel. In the modern yen sign 円 it has lost semantic role and reads as the inner stroke-pattern of the simplified glyph.