It's That Reincarnated-as-a-Virus Story, Volume 2 (It's That Reincarnated-as-a-Virus Story #6-10)

Our protagonist started out infecting a rat and has now infected a hobgoblin. Pretending to be a human, he goes into the city, but immediately gets caught up in some trouble and unexpectedly ends up playing an active role! In the meantime, he forms a party with Elena, who he met again, and starts being an adventurer...?!