I forgot to type up the process of translating this…
“The black dragon lightning comes.”
By itself, 黒龍雷迎 (kokuryuu raigou) is literally ‘black dragon lightning greeting’, “the greeting/welcome (lightning) of the black dragon”. I believe that Akamatsu is referring to 来迎 (raigou) here – the appearance of Amitabha to welcome the newly deceased. With this, I think the intended meaning is along the lines of, “the black dragon welcomes your life’s end with lightning”. Tie this in back with how Dunamis ‘entombed great dragons’ and it becomes pretty ironic.
However, the original 黒龍雷迎 by itself doesn’t actually state this – it’s still just “lightning welcome”. In the end, I didn’t use the literal translation and chose “The black dragon lightning comes.” because it matches the terseness and finality of the original phrase. Basically, downsizing “comes to welcome you” to just “comes”.
Your mileage may vary on whether this was a good choice, but this was my reasoning, at least.