“By the way, Mika-san, have you already gotten to know the people over there?”

“Um, do you mean the bipedal Chihuahua people?”

When Mika asked, Takayuki happily clapped his hands and nodded, saying, “Yes, yes!”

Then, as they ate lunch, Takayuki briefly explained how he had obtained this key.

This happened back when Takayuki wasn’t running a supermarket yet, but a small antique shop. His family were landowners in this area, and the hills behind the antique shop also belonged to the Yamano family. It was Takayuki’s idea to repurpose an old, disused wartime air-raid shelter into a warehouse. He replaced the entrance door, reinforced the inner walls with concrete, and left only the back wall as rough, exposed rock—but it became a perfectly functional warehouse.

One day, as Takayuki was storing some antiques he had collected in the warehouse, he dropped the key he was holding.

Even though there was some light, the warehouse was dim. Takayuki got down on his hands and knees to search for the key, but he couldn’t find it. After over ten minutes of searching, he finally spotted it near the boundary between the rocky back wall and the concrete floor. As he picked up the warehouse key, he noticed something else—a green ribbon buried in the dirt along the edge. When he tugged on the ribbon, he found another key tied to it, nearly identical to the one he had just picked up.

He had no idea where it came from, but assuming someone had accidentally dropped a spare key, he picked it up without much thought and took it home. The next time he went to the warehouse, he brought the key with the green ribbon and used it to open the door—only to find an unfamiliar cave on the other side.

For a moment, he froze in shock, but Takayuki was a curious man who loved exploring mountains and fields, so he decided to venture inside and investigate.

Along the way, he picked up various discarded objects, his heart racing at their antique value… In other words, his excitement over potential profit outweighed his surprise at the bizarre phenomenon.

Deep in the cave, he found a staircase leading upward. Though it was a bit cramped for Takayuki, the ceiling wasn’t so low that he couldn’t pass through. He climbed the narrow, uneven steps two at a time until he reached a fork in the path.

Though curious, he decided not to get lost and continued climbing several more floors. It didn’t take long, but the cave stretched far higher than the hills behind his property, and even he realized he should come back better prepared. So, he turned back.

On his way back through the cave toward the door, he encountered several strange creatures. Fortunately, he managed to fend off attackers with an antique dagger he had picked up along the way and even knocked down a rather large bat that flew at him.

Over the next few years, whenever he had free time, he would enter the cave and continue his explorations.

“I’m sure you’ll be able to interact with the people over there soon, Mika-san.”

With a gentle smile, Takayuki held out his palm, where a single prominent black mole stood out.

Without thinking, Mika also opened her hand and showed it to Takayuki. There, just like his, was a single black mole—a magical mark that allowed communication with the people of that world.