Sins of the Father
Daken attempted to make off with the sword of his father forged by an insane immortal blacksmith. Said undertaking was preempted by the X-Men and the blade ended up splintered as a result. In the aftermath over possession of such however, Daken managed to make off with the tip of said broken weapon and hired a criminal scientist known as The Tinkerer to implant them within his body.
Undergoing a bonding process straight out of the Weapon X program, the atom splitting sabre could be fused to the former's third claw located beneath the forearm. This came with the added catch that said weapon wasn't as sturdy within his body without an Adamantium skeletal bracing, making their usage a double edge sword.
Even exposure to his soft tissues while not in use was potentially lethal as the fragments carried over the healing factor nullification effect of the main vorpal instrument. To prevent said implants from splintering within his wrists after suffering a damaging impact, Phineas implemented a pair of Adamantium sheathes around them in order to protect his internal bodily structure whenever he pops his claws. Daken would attest their effective deadliness while battling the likes of Skaar; the estranged son of The Hulk and all around powerful gamma mutate in his own right.
The monomolecular edge of the Muramasa Blade carried over into the latter's nails, being able to rend and tear through the hulkling's otherwise impervious hide, as well as diminish the Skaar's healing factor to almost nothing.