surname, fresh
尟 is a rare kanji whose meanings are not clearly connected: it can refer to a surname or to freshness. The two senses likely developed independently, so treat it as a character with two separate uses.
The origin of 尟 is uncertain. It combines 是 (correct, this) with 少 (few, little), but the historical relationship between these components and the meanings 'surname' and 'fresh' is unclear.
Imagine a fresh surname written with few strokes: 是 (correct) wraps around 少 (few), like a rare family name that stays fresh through generations.
For セン, picture a fresh cent (coin) with a rare surname stamped on it: cent -> セン, and the coin is fresh and new.