fill, full, satisfied
滿 centers on reaching a state of complete fullness: filling a container, being full, or feeling satisfied as if filled up.
滿 combines 氵 (water) with 㒼, which likely contributes both sound and the idea of being full or covering evenly. The character expresses the concept of water filling a vessel to the brim.
Water 氵 on the left and 㒼 on the right suggest liquid rising evenly until the container is completely full. Picture a cup filled to the very top.
For マン, imagine a man filling a huge water tank until it is completely full: man -> マン, and the tank is filled to the brim.