Why is Seigi's tattoo described as "triggerless"? On multiple occasions, Seigi's tattoo is described as "triggerless" (this is the wording used on Crunchyroll). The first time we hear this is near the end of episode 1, around 22:08. However, when Seigi is talking with Izzy and Tom on the school roof in episode 2, Izzy tells him that his tattoo is triggered by blood. 

It hardly makes sense for a "triggerless" tattoo to have a trigger. What's the deal?

(At first glance, this seems like a translation mishap, since the Japanese word in question is mugen, and I don't know of any way to get from there to "triggerless". But perhaps there's a good reason for this - I've only seen 3 episodes of the anime to this point, so I'm not very knowledgable about Taboo Tattoo.)
The manga refers to it as 無鍵 or "keyless." The anime uses the same term (see the Ep. 3 summary).

As for what these keys refer to, 


    There are actually 4 Void Makers and they are the keys to the Tattoo Ruins. It seems that every Void Maker needs a host to become a "key." So apparently Seigi's Void Maker had no compatible host prior to him,  thus making it "keyless." 


His trigger however seems to be blood.