Goblin Slayer Gaiden 2: Tsubanari no Daikatana is the manga adaptation of the Novel relating how the party of 6 heroes cleared the dungeon of the Dead near Fortress City 10 years before the main story (Goblin Slayer), all above mentioned is in some spare interludes on the Goblin Slayer Light Novel Volume 8. So you better start reading the Light Novel to then enjoy the complement of this spin off manga.

Now it's unfortunate it got cancelled for quality issues and the mangaka starting his own series, I don't blame them because transcribing characters on art is a problem, but many of the issues were half-assed story details and some shonen style manga that will create many chapters instead of reaching to the main plot inside the dungeon, hell, it was cancelled before reaching 5 of the 6 people on the party.

Characters are well done, the world of Goblin Slayer is not relevant on giving them some special details but it worked fine for them. Enjoyment is lacking because you're getting inside a shonen-style manga and giving way too many details that perhaps are mangaka's freedoms instead of the Goblin Slayer formula working like the other adaptations (Side Story, Main Story).

Overall, they did a fine job on creating a world on Fortress City, but the sequel of this manga (the real adaptation) gets the job better and without dropping in details and direct to the action.