There are few, if any. One of them could be the lack of background for some of the supporting characters- however, I have a feeling most of that will be taken care of later on. (I mean, the manga is still publishing and it would be a real bummer if it suddenly got cut off.) No matter how hard I look, besides that, I really just cant find anything wrong with Blood Lad. I mean, I'm literally sitting here, about to make my dad's $3000 PC burn up with my ferocious glares, trying to spot any errors the author did.
Blood Lad really is an amazing piece of work so far- I'm crossing my fingers that the publishers don't rush it and end it crappily, because it's gotten a lovely headstart.
Fashion can be a great way to build verisimilitude in comics, and Kodama certainly demonstrates a facility for fashion in Blood Lad. If the clothes are believable, then there’s one less thing that can eradicate your suspension of disbelief. You buy into the story in part because the fashion doesn’t get in the way. In fact, the fashion makes it stand out amongst a sea of people wearing generic solid colors and lackluster leather jackets.