IMO needs a lot of work:

-text formats, headings, right now it's kinda wall of text;
-more general info regarding effects like character attack vs elemental attack (when one is better than another and why), main/sub eidos and summon/passive effect, friends/non-friends eidos, mention that non-friends eidos passive actually works etc.;
-maybe some eidos orb shop info;
-you already started this but make the division more distinct - rarity (R-SR-SSR)/how to get (gem or jewels/prem gacha/events/story quest drops/materials exchange shop) /passive effects (like 30% chara atk/ability DMG, 30% chara/30% burst-streak DMG, 40% chara/20% HP etc.);
my suggestion is smth like this: first goes rarity, then how to get - basically just 2 options (f2p and permium), maybe add detailed for each eido later, then group them by passive effects; after that list element, atk/hp stats, summon effect and do a basic analysis like 'meh passive, good summon, nice stats, useful as sub eido';
-probably the most important - TERMS, just a few examples:

...St. Nickolas- She gives a nice increase to the attack power of light characters...
...Reiki- She’s pretty much like Jack Frost, but done a different way. She increases water character’s attack power...
it's all over the place; the "attack power" you use is confusing as hell, you have to use either "character attack" or "elemental attack";

Jack Frost part:
...This means one of the dots gained during an enemy taking a turn can disappear...
maybe it's just me but when i read that i thought about DoT (damage over time) and not about overdrive charge orbs;

-small addition to formatting/grouping eidos part and why i thinks that's important - to avoid stuff like this:

...Echidna- She’s the same case as Ouroboros...
...Fafnir- Same case as Echidna...
...Huanglong- She does the same increase as Hecatonchires...
...Jabberwock- She does the same increase as Ifrit...
...Fenrir- She does the same exact effects as Ifrit...
...Reiki- She’s pretty much like Jack Frost...
...Amphisbaena- She’s like Jack frost...
...Icarus- She’s like Reiki...
literally just all the way thru the SSR part. Maybe that's the way guides need to be idk, but personally i'm not a fan of this stuff. I prefer things to be short and on-point.