精 (Kanji for spirit)

I'm almost wanting to say SIDEKICK since ９0％ of the time it's only used with 精神

Onyomi

SEI

If your body doesn't eat enough rice, your spirit gets mighty blue.

精神(せいしん)

spirit ★★★★☆
精 (spirit) + 神 (GOD kanji) = 精神 (spirit)

spirit- both in the sense of psychology and in the sense of religion. If you want to say "Samurai spirits!" this is the one you'll use.

精一杯(せいいっぱい)

with all one's might ★☆☆☆☆
精 (spirit) + 一杯 (one cup-full) = 精一杯 (with all one's might)

精神的(せいしんてき) な

spiritual. ★☆☆☆☆
精神 (spirit) + 的 (motivation / '-al') = 精神的 (spiritual.)