I'd go Japanese. You get a lot more art for the same price and their politics don't align with ours. So the weird political shit (and it is in there) kinda just goes over the head.

Also, the plant thing, not that creative. I think Evil Dead 2 had a chick being murder raped by a possessed tree. And it wasn't unique then.

My vote;

https://www.amazon.com/s/ref=nb_sb_ss_i_1_11?url=search-alias%3Dstripbooks&field-keywords=warrior+nun+areala&sprefix=warrior+nun%2Cundefined%2C696

and Yes, Catholic School boy here :)

What if it's a plant?

Well..

https://www.amazon.com/Creamed-Butt-Handsome-Living-Corn-ebook/dp/B01A4E0MD6#nav-subnav

Joke aside, the Blacksad graphic novels are an interesting noir read:

https://www.amazon.com/Blacksad-Juan-Diaz-Canales/dp/159582393X

Get them any of the novels except Arctic Nation, that one is great novel with references to the segregation era and the hangings. That one not a good recommendation for kids because of a uh, vignette that has sex and you don't want the parents of the kids to blame you for their interest in furry stuff.

The Watchmen

Well, there's Asterix and Obelix books. No tits, no sex, and overly sanitised profanities.

There's dozens of them and it's different from the overly ripped American graphic novels.

You can also gift them this:

https://www.amazon.com/Hell-Beasts-Grotesque-Fantasy-Creatures/dp/1581809263/ref=pd_sim_14_7?ie=UTF8&psc=1&refRID=41Z91S2DZ4H81CN5ACHC

How to draw grotesque monsters? That is probably the next best thing (except nudes) for a kid in that age to draw.

If you can find one, A Redtail's Dream by Minna Sundberg is absolutely the best coming of age graphic novel I have read. Unfortunately it was a limited edition print, and I'm not seeing any copies on ebay at the moment. It is available for free online.
I personally like the DR. McNinja omnibus, but that is not to everyone's taste.

Two great modern ones which are wholesome are any of the Atomic Robo series or the new Squirrel Girl. Humorous action packed. No nudity. Atomic robo is slighlty more cynical and Squirrel Girl slightly more innocent, but both are great.

Clive Barker's "The Yattering and Jack".

Thanks for these recommendations! Really appreciate them!

They might enjoy "Grease Monkey".

Gotta recommend Jeff Smith's "Bone." Fabulous comic/graphic novel for all ages.

https://www.amazon.com/Bone-Complete-Cartoon-Epic-One/dp/188896314X/ref=sr_1_1?s=books&ie=UTF8&qid=1473456738&sr=1-1&keywords=bone+jeff+smith or https://www.amazon.com/BONE-1-Boneville-Jeff-Smith/dp/0439706408/ref=sr_1_2?s=books&ie=UTF8&qid=1473456848&sr=1-2&keywords=bone+jeff+smith

I almost forgot. Here's something from South America:

https://www.amazon.com/s/ref=nb_sb_noss?url=node%3D4366&field-keywords=quino

Quino is a cartoonist whose political drawings have a tendency to be timeless mostly because his attacks had to be vague, otherwise the Argentinian government/military would have him suicided.

For easy reading don't pick the Mafalda unless you (or the twins) already know Spanish and knowledge of the era (Pre-Beatles up to the 1970s).

300. Harlem Hellfighters (WWI). 13 year olds are too old for Asterix.

Are you buying them manga because the pweshuss widdle flowers are products of the 'Murican educational system Are they short attention span, functional illiterates incapable of reading a real book? Jeeze, when I was 13, I was getting my reading material from the adult section of the library, in spite of the efforts of the old bat librarians to limit me to the mindless Bowdlerized kiddie section crap.
Get them CS Forester, old school SF, Asimov, Clark or Simak, noir genre mysteries, popular histories with enough blood and thunder to keep them interested.
Oh, never mind, that might start them thinking, that is if their brains have not already been irreparably mushed, and boys who think get into trouble for harboring non PC thoughts.

"Faust" -- Classics Illustrated from 1962.

https://www.amazon.com/Faust-Classics-Illustrated-Comic-167/dp/B004E9VI68

f you go with books get Starship Troopers and Job: A Comedy of Justice

Everyone should read Heinlein