Lie. Tell him it's all about happiness and joy and all this other crap. /sarcasm.
But in all seriousness, just lay down a synopsis that goes something like:
'In a world where men don't die, and women are as chaste as ever, there is one who dares to stand against it! HIS NAME IS GATTSU! The Black Swordsman!'
Gomen, gomen. I can't help it. I'm hyped up on sugar.
But to get him interested...humn. What does he like in a manga? Try telling all the sell-sell points of it, like the political intrique, the violence, the excellent story...the characters! The arcs! Really, just..try to warm him up to the idea, and let him read a few chapters; hell, read him a chapter from way in the future of Berserk, that's mysterious and sort of cliff-hangy. That might get him on edge and want to read from chapter 1 all the way through.
Try all different methods~ Except for the two I posted before my sensible one's. Those were just me being sarcastic, and I apologize.
-Kiri.