Venetica

This is a fairly easy achievement. What you need to do is go to the Holy Seal headquarters in the Outer City region of Venice. You can do this immediately after the conclusion of Chapter 1.

Once there, speak with Rangar. Inquire about joining the Order of the Holy Seal, and he will send you on a quest of the same name. This will take you to the catacombs underneath the Outer City. If you've played ahead, this is also the same place that the quests "A Gardener's Nightmare", "Damage Underground", and "The Gripper Queen (Outer City)" take place. The latter quest will also earn you the Gripper Queen Slayer achievement.

Once you return to Rangar with the shield item, you will become a member of the Order of the Holy Seal and the achievement will pop!

Note: You can only join one guild per playthrough, so choose wisely. Also, even though you are required to talk about vengeance with Rangar to join the guild, you can still earn the "good" ending.

Also, you can earn the Trained Blocker achievement from Rangar before or after joining the Order. You can earn the Trained Group Fighter achievement after joining the Order.