Kindness.
It was by far his greatest virtue. Armed with his kind heart, a frying pan to cook excellent meals, and an apron to keep his front clean, Klaus Becker had progressed through the underground in a way quite unlike any human before him. Opposed to needing to be escorted through, or protected by certain monsters until brought to King Asgore, he had simply shown his immense kindness in the only way he knew how to; through cooking.
Through the Ruins he had traversed, and while he was unaware of how desolate it may have seemed to the previous children, to him he had met many monsters. The obvious Froggit, Whimsun, and Vegetoid (though he only learned of their existence when he'd nearly picked one for a stew. It had taken many profuse apologies to get it to calm down), but he had also met the lonely widow within as well.
He could sense a great sorrow inside of her that prompted him to try and cheer her up by simply cooking her a nice meal. To his surprise, she was skilled with a stove as well, and they wound up having a fun cook-off together. She'd commented on his extraordinary kindness, but had been apprehensive when he'd expressed a desire to move on. Eventually, she relented, packing him a bag with all the goods they'd baked and asked him to spread his kindness through the underground.
So he had done just that. Through the snowy forests he'd trekked, encountering a whole slew of dog monsters, all of which he'd befriended through food and a few simple games of catch. Past them, he'd moved on through Snowdin and shared his cuisine. Whereas the lonely widow had recognized him as a human immediately, most of the monsters elsewhere didn't seem to realize he was human. Perhaps they'd never seen one.
Beyond Snowdin, his path led through the great glowing caverns, where he encountered his first conflict; Flouis Dhelaron, Captain of the Royal Guard. He was an elderly monster with a spring in his step, and seemed to really hate humans, recognizing Klaus immediately.
When he'd refused to be escorted directly to the king, his goal the lonely widow having given him still in his mind, Flouis had attacked. Their battle raged on, but his kindness eventually broke through, and Flouis relented, allowing him to progress beyond and into the Hotlands.
There, he'd met the Doctor who seemed even more intimidating than Flouis. Just like the Captain, the Doctor offered to bring him to the king, but hadn't attacked when Klaus had declined this. Instead, he offered directions, before retreating into his lab, not accepting the goods offered.
So he had moved forward, steadfast and confident that the lonely widow's request would be fulfilled. He was nearing the capital, and had shown such kindness to the monsters underground. She had warned him of their hatred toward humanity, so perhaps he could change their mind. She seemed to think he could.
His journey took him through the remainder of Hotlands, alongside a town on the edge of the capital known as 'Warmville'. It was somewhat silly how simple all the names were down here, but he found it incredibly charming. He had fed and befriended the monsters here as well, until moving upon the capital to find that it was far more populated than even Purple Home, where the lonely widow had lived. This would require far more food than he had left, so he did the only logical thing there was to do. He found the nearest shop, and offered to cook new and exquisite meals. The store owner, a large and wide golden reptile, had been skeptical before allowing it.
It took no time at all for the store's popularity to explode as the underground was introduced to human cuisine.
He'd been offered to work full time at the restaurant, and it was an extremely tempting offer, though his mind traveled back through his journey. He'd been warned of King Asgore by the lonely widow. The Captain had desired to take him there and even battled him for it, the Doctor too wishing to deliver him. He knew he was fated to meet this King soon, and he even glimpsed his majestic castle on his walk through town.
