The poisoning at least explains why Kaito is so tired and why his wound is not healing properly.
The venom of the Silk Bulb Spiders is known to be very powerful, no wonder in the past Kaito visited this place twice just to look for it before everything collapsed. As such, Kaito is lucky that he is a vampire and therefore doesn't suffer from the poison as much, because for other people it could be deadly. Regardless, he knows he needs to act quickly to neutralize the poison in order to continue his exploration.
He knows he can use <Life Drain> to drain the life energy of other living beings to heal himself, but that probably won't nullify the poison. So, he needs an antidote. Normally, he would need to go up to the city and look for an alchemist's store, but now he has another alternative.
"Open Merchant's Shop." utters Kaito.
Suddenly, a system window opens before his eyes.
[Welcome to the Merchant Store Stock! There are many items available!]