This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 裧 is uncertain. It visually combines 衤 (clothing) with 炎 (flame), but the original semantic and phonetic roles are unclear.
Since the meaning is uncertain, focus on the shape: clothing 衤 beside flames 炎. Imagine a garment that is fire-resistant or used in a fire ritual, but treat this as a memory aid only.
For セン, picture a ceremonial sen (千, thousand) robes being purified by flames: 千 -> セン, and the clothing 衤 meets the fire 炎.