“alone / sole” in Japanese is 独, read doku, hito (どく, ひと). It is a Grade 5 Kyōiku kanji, taught in year 5 of Japanese elementary school, and appears in words such as 独立 (independence).
What does 独 mean?
弟は独りで遊んでいる。
Same sound, different character — the classic trap. Compare them side by side: