hold up
袺 centers on the action of holding something up, often with the hands or by using clothing as a receptacle.
袺 combines 衤 (clothing) with 吉, which likely contributes the sound. The character is rare, and its exact historical development is uncertain.
The clothing radical 衤 suggests using a garment to hold something up. Picture lifting the hem of a robe to carry items, with the right side 吉 representing the good fortune of not dropping them.
For ケツ, imagine holding up a heavy kettle with your robe: kettle -> ケツ, and the cloth helps you lift it.