Maldan Byeongsaeseo Gunjukkaji

When Chris, a one-armed mercenary with considerable experience and skills, swallows an artifact after an unlikely encounter with a savage looter, he finds himself back in the past as a 15-year-old lowly foot soldier... with both his arms. This time, he will not let his life take an unfortunate turn. This time, he will not let his friends die in vain. This time, he will use his knowledge and reach for the sky.
(Source: WEBTOON)
Note: Includes five extra chapters.