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.
Crowning Music of Awesome: There are 3 piano pieces that this anime produced that are especially noteworthy for the beauty of the compositions, to the point that many pianists cover them. The first two are arrangements of the opening themes, For Real and Alone, while the third is Hakkai's Theme.
Foe Yay: The anime (especially the first season) implies that Hakkai may harbor romantic feelings towards Yaone.
Fridge Horror: In Saiyuki Ibun, Genkai's best friend Toudai is the only one not afraid of touching him. Touching Genkai reveals your future to him. Now consider Toudai's ultimate fate as revealed in Burial. Genkai had to live with knowing all along the brutal way in which his best friend would die. Seems kinda merciful that Houmei goes out of his way not to touch him now, doesn't it?
Fridge Brilliance: Not that Ukoku really needed any more reason to try to Ret Gone Sanzo in Reload, but there's an even more pressing reason than Ukoku's love of mind-rape, wanting to win his bet with Koumyou, and trying to stop Sanzo interfering with his plans. Ukoku was obsessed with Koumyou, who was the only one who was ever able to get the better of him but refused to fight him straight out. He is extremely bitter that such a man died for some brat when he should have been able to defend himself easily from those bandits. Ukoku's conclusion is that Koumyou committed suicide by those attackers, in order to set Sanzo on his path. Ergo, Ret Gone -ing Sanzo would BRING KOUMYOU BACK TO LIFE.
Foe Yay Shipping: Yaone and Hakkai are a popular pairing. Lets not forget Kougaiji/Sanzo, which is popular, Kami-sama/Sanzo, which is less popular but exists, along with the squicky-er chin-Yisso/Hakkai, and Dokugakuji/Gojyo. Homura/Goku, Homura/Sanzo, Dougan/Sanzo. If you can count Hazel as an enemy, Hazel/Sanzo (he definitely is in the anime, but the manga less so). Li Touten comes on to Tenpou (which is why he flips) Nataku and Goku are friends but are pitted against each other, and Kenren and Goujun's fight has some elements of this as well. It's safe to say this manga is full of it.
Moral Event Horizon: Gyokuman Koushu crosses this repeatedly, having started the release of minus-waves to revive Gyomaoh, and we later find that they were started on PURPOSE to make the youkai more violent so they would be more likely to bring her the scriptures that she needed to revive him. She still has more moments with implying that she plans to sacrifice her own daughter to revive Gyomaoh.
Villain Decay: Poor Zakuro didn't even make it to the end of the chapter before the decay started ...