These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Ayashi no Ceres
Awesome Music: The opening (Scarlet) and the second ending (Cross my heart).
Creator's Pet: Toya. Confessed by Watase, although it's not like she ever hides this kind of things. However, Toya deserves a special mention because he's still her favorite pet ever, even to this day.
Fan-Preferred Couple: Many people consider Yuuhi to be a better match for Aya than Tooya, though she actually does sort of end up with him. Not on-screen, but considering Tooya is dying already and he asks Yuuhi to protect her once he does... Other fans thought that Yuuhi's attempts at romancing Aya could've used a lot less Attempted Rape.
Magnum Opus: Apart from Fushigi Yuugi it has no real contenders for the title of Yuu Watase's magnum opus, and if we're counting pure storytelling skill and drawing proficiency then it beats Fushigi Yuugi as well.
Narm: In the anime, the scene where Tooya is tortured to almost death via being repeatedly gunned down by Aki possessed by the Ancestor is so ridiculously dragged-out that it becomes a borderline Overly-Long Gag.
Strangled by the Red String: Aya and Toya's relationship comes across as this because they've had such little interaction until Aya is taken to his apartment and suddenly declares that she loves him. Somewhat justified by the fact that he's an evolved life form made out of a divine energy ball and was basically wired to serve and protect her family, hence the instant love can be seen as an application of this instinct. The fact that his dad was an old hermitdidn't help his relationship skills.
What The Hell, Costuming Department?: The Celestial Maidens' true form when they are fused with their Mana. In-universe the characters react like they look alien, but godly beautiful. The reader... might disagree...