Seraphim

Seraphim was a top Guild that existed in YGGDRASIL.

Background
Seraphim was considered as one of the top guilds in YGGDRASIL. The guild was known to be quite selective on their membership and it only accepted angel-types into its ranks.

Overlord Prologue (1st Half) Arc
While Momonga and Peroroncino headed toward to Nine's Own Goal's meeting they talked about their plans in achieving their dream builds. Peroroncino was skeptical about the source of Momonoga's information on the data crystals necessary for his dream build, however the latter claimed that the information came from Seraphim.

Overlord Prologue (2nd Part) Arc
After conquering the Great Tomb of Nazarick and being rewarded with a World Item, one of Ainz Ooal Gown's guild members boast about their achievement and mock Seraphim.

The Craftsman of Dwarf Arc
Ainz considered that the Regency Council's wariness to be understandable, because he also shared the exact sentiment as them. In this case, he imagined the event where if Seraphim, an infamous guild were to use a World Item as bargaining chip for negotiation, he would be suspicious of them and think it is a trap put in place to sabotage a person or group.

Strength
Due to its prestige and popularity, Seraphim's information on YGGDRASIL was considered to be undoubtedly credible. On the other hand, Ainz thought that if the top-ranked guild, Seraphim offered a World Item as part of a trade deal on the negotiating table, he would definitely suspect it to be some kind of trap set up. This could hint on the possibility that Seraphim may in fact, most likely possessed a World Item of their own.

Trivia

 * The guild is named after a class of high-tier angels that are said to be the closest to the Throne of God in Heaven.