go, reach, appropriate, suitable
适 centers on movement toward a destination or state: going, reaching, and by extension, arriving at what is appropriate or suitable.
适 combines the movement radical 辶 with 舌, which likely contributes the sound. The idea of going or reaching is carried by the movement component.
The movement radical 辶 suggests traveling, and 舌 (tongue) can be seen as something that reaches out. Imagine a tongue stretching forward to reach a destination, making the journey appropriate.
For カツ, picture a cat reaching out with its tongue to catch a treat: cat -> カツ, and the tongue 舌 stretches forward along the path 辶.