Ihoujin, Dungeon ni Moguru

It was in 1946 that Earth learned of the existence of other worlds. As expected, many countries immediately tried to send people into the other world, hoping to obtain vital resources or mystical treasures. None of them came back.
And to be fair, Souya never expected to be one of those explorers. But here he was, accepting an offer by a shady company to get enough money to save his little sister. Launched into another world, he soon finds that his journey will be a hard one – not only have his teammates gone missing, but a majority of his food and weapons supply was destroyed in the transfer.
The only way left to go is forward. With only an AI companion to guide him, Souya ventures forth, hoping to find something worthwhile that will justify sending a rescue party to save him – if such a party comes at all.