Disclaimer: This idea was born from Anime/Hentai memes and a binge of MythyMoo's Metal Gear Rising playthrough on YouTube. Also, i'm only using the D and D God of Justice's name, apologies for the unoriginality
When Raiden closes his eyes in order to reflect on the Desparado incident and everything that had come of it, he hadn't expected to open his eyes to a vast white void of nothingness and a strange white haired man sitting atop a gilded throne.
The man introduces himself as Amuanator the "God" of Justice, and he makes Raiden an offer.
10,000 years of servitude, traveling the multiverse and saving poor misfortunate souls from their unjust ends, and in exchange Amuanator would replace his cyborg body with a mortal body just as powerful.
The offer could be bullshit, no it probably *is* bullshit, or some kind of hallucination caused by someone hacking into his body, but the thought of being able to truly feel the warmth of Rose's body against his own, to be able to hold his son in his arms and not worry about giving him static shock or accidentally hurting him because someone had the bright idea of hacking into the Mil Spec Cyborg is too good to pass up, and so after what seems like hours of deliberating he accepts the "Gods" offer.
And thus begins the journey of a Cyborg Ninja, traveling the multiverse and righting wrongs in the only way he knew how, and his patron God, tired of all the suffering the denizens of the multiverse were forced to endure because of the inaction or deliberate actions, of so many of his godly brethren.