thin kimono, undergarment
襌 centers on a lightweight, single-layer garment worn close to the body: a thin kimono or undergarment.
襌 combines the clothing radical 衤 with 單, which likely contributes the sound and the idea of something single or thin. The character specifically refers to a thin, unlined garment.
The clothing radical 衤 beside 單 (which suggests single or simple) gives a single-layer garment: a thin kimono worn as an undergarment.
For タン, imagine a thin tan-colored undergarment: tan -> タン, and the clothing radical 衤 reminds you it's a garment.