Various Levels and Grade Classifications.

Power levels

Tier 1 – Low-class Devil/Angel

Tier 2 – Mid-class Devil/Angel

Tier 3 – High-class Devil/Angel

Tier 4 – Ultimate-class Devil/Ten Seraphs

Tier 5 – Satan class/Four Great Seraphs/Dragon Kings

Tier 6 – Super Devils/Evil Dragons(Only a few of them)/High-level Gods.

Tier 7 – Heavenly Dragons/ Highest-levels Gods such as Shiva, Ophis and Lilith (after Ophis's power was divided in half)

Tier 8 – Dragon Gods/True Dragon/Trihexa(666)/ God of Bible (possibly)

Tier 9 – Highest level of DxD world.

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Grade of skills and items.

Common << Uncommon << Rare << Ultra Rare << Unique << Legendary << Divine << Immeasurable.

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Energy value of each level. (Mostly mana)

Low-class: 10 – 100

Mid-class: 100 – 1,000

High-class: 1,000 – 5,000

Ultimate-class: 5,000 – 50,000

Satan-class/Four Great Seraph/Cadre/Dragon Kings: 50,000 – 150,000

Super Devil/High-level Gods/Evil Dragons: 150,000 – 450,000

Heavenly Dragons/Highest level Gods: 450,000 – 999,999

Dragon Gods/Trihexa: One Star (Having energy equal to a star, often considered boundless.)