Specifics
Odoru Baculogypsina

Series: Fate/Extra CCC

Pairing: Gilgamesh/Hakuno

18+: Yes

Under My Feet

Series: DMC Devil May Cry

Pairing: Dante/Vergil

18+: Yes

Saiai no Tomo
(A Beloved Friend)

Series: Fate/General

Pairing: Gilgamesh/Enkidu

18+: Yes

General
These are the series I'm open to suggestion from. I've put the specific pairings/characters I'm interested, but I'm generally very open to - if not very quick with - suggestions of any kind for these, so it never hurts to ask! This list is hardly all-inclusive.
Breath of Fire IV
Fou-Lu centric

Legend of Zelda

Yu-Gi-Oh!
Bakura or Thief King centric.

Final Fantasy XII
Balthier Balthier Balthier. And Fran.

Final Fantasy VII
Vincent, Reno, and/or Turks centric.

Grandia

Tales of Vesperia
Yuri centric.

Tales of Symphonia
Kratos centric.

Tales of Berseria
Eizen centric.

Tales of the Abyss
Asch centric. Asch/Luke, Asch/Natalia if it's not boring.

Tales of Xillia
Gaius-centric, Milla's awesome too.

Castlevania: Lords of Shadow

El Shaddai
Lucifel/Enoch, Lucifel-centric,

Devil May Cry
Specifically hunting for DMC, but anything Vergil-centric is nice.

Fate
Gilgamesh, especially Caster!Gilgamesh
Assassin of Shinjuku/Yan Qing
All the CuChulainns
Richard I
El Melloi II

-Star Ocean 3
Albel-centric.

Star Ocean 4
Arumat-centric, or Faize/Lymle

Xenosaga
Albedo-centric, Albedo/Jr. if it isn't excessively creepy.

Arc the Lad: Twilight of the Spirits
ANYTHING but Darc is my favorite.

Black Blood Brothers
Zelman-centric

Majin Tantei Nougami Neuro

Assassin's Creed: Syndicate

Dragon Age
Fenris, Solas, or Abelas

Thor
Loki

Batman
Damian, family cuteness
Batman Beyond!

Spider-man

Avengers
Loki, Namor, Hawkeye. Not necessarily together, though that'd be awesome.

X-Men
Gambit, Daken, Quentin Quire, Namor.

Anything Marvel, really

Dishonered
Outsider-Centric

Horizon Zero Dawn
Nil would be fun, but I'd take anything I think

Lupin III
Lupin-centric

Inuyasha
Sesshoumaru/Kagome or any of the Shichinintai-centric

Voltron
As long as Lotor is involved and treated well I'd be happy

How To Train Your Dragon
Family cuteness, very specifically looking for PG stuff