This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
偱 combines 亻 (person) with 盾 (shield). The exact historical development is uncertain, and the character is rare in modern Japanese.
A person 亻 beside a shield 盾 could suggest someone protected or shielded, but the true meaning is unclear.
For シュン, imagine a person named Shun holding a shield: Shun -> シュン, and the shield protects him.