The Seraphim were specifically designed to replace the Seven Warlords of the Sea within the dynamic of the Three Great Powers.

They are clones of the former Seven Warlords of the Sea created using the Lineage Factor, but are larger in size compared to the original people they were cloned from. In particular, S-Hawk—the Seraph based on Dracule Mihawk—exhibits an incredibly destructive level of swordsmanship that is capable of splitting even mountains in half, not unlike Mihawk himself. Pythagoras theorizes that this might be a property of the Lineage Factor, which could potentially transmit memories of learned skills from the original individuals unto their Seraphim counterparts

The Seraphim also appear to be modified to possess lunarian appearance and traits, including the ability to ignite. Like natural Lunarians, the Seraphim are capable of becoming drastically faster when their flame goes out, but will become more vulnerable to attacks.The Seraphim undergo an accelerated growth process and are infused with a substance called Green Blood which can be instilled with the lineage factor of a Paramecia-user, allowing that unit to emulate the Devil Fruit abilities of the said user such as S-Snake’s Mero Mero no Mi, S-Shark’s Sui Sui no Mi and S-Bear’s Nikyu Nikyu no Mi.

Due to all the technology that must be invested in their creation and maintenance, the Seraphim are considered extremely expensive to make. This could be attributed to the fact that Lunarian DNA is hard to come by, along with the materials used to create them. Thanks to their numerous unique traits, they are considered by their inventor, Vegapunk, to be the highest echelon of science conceivable, even referred to by him as The Strongest Form of Humanity in the history of the sea.

Though artificially created, their biological nature means that the Seraphim are apparently capable of aging and thus becoming stronger as they mature. They have shown enough strength and skill to force even one of the Four Emperors, Marshall D. Teach, into a defensive position, right after effortlessly defeating a myriad of his subordinates.

Also, thanks to their lunarian traits, they appear to have vast resilience, something noted by the Gorgon Sisters, who claimed the Seraphim involved in the siege left the island with nigh a scratch over their bodies. Their young appearances may also inhibit foes who have reservations fighting children from attacking them. Helmeppo would later infer that sending even a single Seraphim against the Blackbeard Pirates would be enough to at least safely rescue the captured Koby from them.

Source: https://www.opfanpage.com/2022/12/27/the-strongest-form-of-humanity-in-the-history-of-the-sea/