The Old Man of the Otherworld's Convenience Store is Actually the Strongest

Starting today, I'm Land, and I'll be working at 'Powson', Nice to meet you.
In a town far from the royal capital Apollonia, there was a 24-hour magic tool shop (convenience store). It was a convenient place for adventurers on expeditions to restock items, potions, and weapons without worrying about the time.
Land, a new part-time worker at the magic tool shop 'Pawson' (with an hourly wage of 900 Nils), had only been working there for a week. Unable to memorize the massive manual, he was causing trouble for his younger, more experienced colleagues.
His dream was to travel the world leisurely in his old age. However, he was on the verge of being fired from the part-time job that was supposed to help him achieve that dream. Today, he messed up a customer's order again and got scolded by his senior coworker, Rick...
But this seemingly incompetent part-timer had a surprising secret...
This heartwarming story depicts the interactions between an old man hiding his true identity while working part-time, and his young colleagues at a convenience store in another world.