I think there was an explanation given that master airbending tattoos go along chi points or hit every chakra or something. That would explain why they get glowy.

The arrows flow along the chi paths of the body. I think if any Avatar gets chi-path tats, they might glow, but we're never shown.

Cause it looks cool.

I mean, you can extrapolate and all you want about "chi" paths and whatnot, but it's pretty much because it looks neat.

To achieve glowy tats, simply mix the ground-up cremated remains of Sparklepyres with your tattoo ink. SIDE-EFFECTS WARNING: May cause skin sensitivity, loss of masculinity, and the desire to mope around looking pretentious.

It's not the tattoo, it's what the tattoo embodies.

I just imagined an Avatar with a glowing tramp stamp.

>>79648
Ya know, where does the tattoo running down their back stop?

Does it stop in an arrow also? Like, at their butt. So... they have an arrow pointing at their butt?

>>79652

I think it splits at the "water" chakra and goes down the legs. Energetically speaking, it would make sense. And this screencap leads me to believe that as well.

>>79648
Nah, if anything they'd have one of these.

>>79655
Well, I remember him saying in the pilot (voiced by Michel Musso, apparently) "It's in the legs."

Which, I suppose is fundamental for Tai-Chi, so eh.

>>79657
Wrong, that tattoo clearly belongs to Zuko.