Taboo Tattoo Series by Shinjiro

By all accounts, middle schooler Seigi is pretty unremarkable except for his martial arts prowess and a desire to protect the weak. But when his good intentions are put to the test by saving an old homeless man from some street thugs, the mysterious man shows his gratitude by...burning a tattoo onto Seigi's palm?! It turns out, the tattoo is a powerful secret weapon that everyone--including a formidable girl with a tattoo of her own--is after... moreBy all accounts, middle schooler Seigi is pretty unremarkable except for his martial arts prowess and a desire to protect the weak. But when his good intentions are put to the test by saving an old homeless man from some street thugs, the mysterious man shows his gratitude by...burning a tattoo onto Seigi's palm?! It turns out, the tattoo is a powerful secret weapon that everyone--including a formidable girl with a tattoo of her own--is after. With his life on the line and his martial arts skills alone no match against super-powered foes, will Seigi be able to unlock the latent potential of his tattoo and live to fight another day?! less

Enlisted by the American military officer Easy, Seigi trains diligently in an effort to master his Spell Crest. But when a friend and colleague of Easy's is targeted in a war brewing over these superweapons, do Seigi and his partner even have a prayer of surviving their next encounter with the agents of Selinistan?

Seigi's Spell Crest is unique in how it creates voids that can cause severe damage to the surrounding area...At least, that's what everyone thought. But now it seems like Princess Aryabhata of the kingdom of Selinistan, as well as the mysterious man called BB, also possess "Infinite Spell Crests" just like Seigi...?!

A year has passed since Seigi went into hiding and began his new life with Professor Wiseman, and something about him has changed. Compared to the old Seigi, he's tougher, colder, and more aggressive. As he defends his hideout from an attack, he receives a challenge from the princess herself! The time has come for Seigi to show off the fruits of his training-a grand battle in the Grand Canyon awaits!

After a year of diligently preparing with Doctor Wiseman, Seigi finds himself locked in a life-or-death struggle with Princess Aryabhata at the Grand Canyon! How will their lengthy rivalry come to a close!?

The long-awaited battle between Seiji and Princess Aryabhata begins in the Grand Canyon! Will Seigi be able to control his emotions, or will his hatred get the best of him?