pleat, fold, tuck, crease
襀 centers on fabric manipulation: creating pleats, folds, tucks, or creases in cloth.
襀 combines the clothing radical 衤 with 責, which likely contributes the sound. The character is a phono-semantic compound where 衤 indicates the meaning relates to clothing, and 責 provides the reading.
The clothing radical 衤 on the left suggests fabric. The right side 責 looks like a stack of folded layers. Picture a garment with neat pleats and folds, each layer tucked into place.
For セキ, imagine a tailor carefully pressing a pleat with a hot iron, making a sharp 'seki' sound as the steam hits the fold: seki -> セキ.