Tegirekingawari ni Watasareta Tokage no Tamago, Jitsu wa Dragon Datta Ken

Yuto Dryg, a young man working as an odd-jobs handler for the advanced guild "Black Thunder," is blamed for the failure of a mission from a nobleman and gets fired from the guild. All that's left in Yuto's possession is a weak magical beast Rock Lizard egg that the Guild Master forced on him, saying, "This is your severance pay"... However, what hatched from that egg wasn't a Rock Lizard, but a legendary Dragon!? A buddy fantasy where a good-natured young man and the strongest baby dragon rise to the top!

(Source: AlphaPolis, translated)