
Ryo sometimes looks up at the moon and thinks of Yuzuki, and on Valentine's Day he makes crescent chocolates for her and sun-shaped ones for Asahi.
In I Want Your Mother To Be With Me!, Yuzuki's name has the kanji for "crescent moon" and her son Asahi's has the kanji for "sun". Though purely symbolic, the ability's main effect is that the surfaces will explode if the sun marker and the moon marker touch. #DEAD BY DAYLIGHT DARK MOONLIGHT VS BRIGHT MOONLIGHT PLUS#
Invoked in Hunter × Hunter with the ability called Sun & Moon: Paired Destruction, which puts a marker of a sun with a plus symbol on one surface and a marker of a moon with a minus symbol on another. This continues on through to three other characters - Tsubomi (who, as Cure Blossom, contrasts Itsuki), Erika (who, as Cure Marine, is said to contrast Yuri) and the Dark Precure who is Yuri's "sister". Especially telling as their personalities contrast one another (Itsuki's more friendly and outgoing while Yuri's quieter and reserved). Heart Catch Pretty Cure has Itsuki and Yuri, Cure Sunshine and Cure Moonlight respectively. Kimblee has alchemic circles on his hands that feature the sun and moon. In Fairy Tail, two of Eileen's subordinates are named Juliet Sun and Hein Lunesea.
In Demon Slayer: Kimetsu no Yaiba, Michikatsu Tsugikuni, great demon slayer of the Sengoku Period, eventually betrays his own humanity and becomes a demon, all for the increasing jealousy he held over his twin brother Yoriichi Tsugikuni for being so incredibly strong to the point Michikatsu thought it was simply unfair to never be comparable to his own younger twin, that reflects on his sword style, called Moon Breathing, being in the shadow of Yoriichis Sun Breathing. It's also lampshaded that Sakura's power is neither that of the sun nor the moon, "but your own mere power of the stars." Eriol's replacement familiars, Spinel Sun and Ruby Moon, have the same degree of contrast in their personalities but running in the opposite direction. Kero and Yue have strongly contrasting personalities and powers, befitting this split - Kero is both figuratively and literally firey, and Yue can be cold and distant. Cardcaptor Sakura has the eponymous cards each being of solar or lunar aspect, and ruled by either Cerberus ( Kero) for the sun or Yue for the moon. (It might also have something to do with certain other twenty-eight-day cycles.) In fantasy fiction, this duality is often manifested in a contrast between a solar God of Light and a God of the Moon. According to Wikipedia, it is somewhat more common to view the sun as male and the moon as female due to the prevalence of that portrayal in Greek and Roman religion. In historical religions, the sexes associated with the sun and moon vary greatly, and in some cases, both a male and female deity may be ascribed to a single celestial body. For example, the pairing could be a masculine and harsh sun paired with a feminine and soft moon. The sun and moon have also been personified by having both of them be a specific sex. See Night and Day Duo or Male Sun, Female Moon if this contrast is evident in a pairing of characters. Given that the sun is a fiery ball of energy and the moon is responsible for the tides, this trope can also lend itself to Fire/Water Juxtaposition. Light/Darkness Juxtaposition can apply when the moon is associated with darkness and the sun with light. Compare Red Oni, Blue Oni and Elemental Powers. The contrast between the two is a common Cosmic Motif (and color motif, particularly yellow and purple, if not outright black and white). The moon does give light in the darkness, and just because it's less constant and more mysterious doesn't make it bad.
Can also go in line with Light Is Not Good, although it can go with Dark Is Not Evil when dealing with characters like Friendly Neighborhood Vampires. Lycanthropes, the most famous example, are depicted as having their transformations trigger when the moon is full. On the other end of the spectrum, the moon also has connotations of light, but it's been associated with The Undead and other supernatural creatures. This can get even worse with monsters and antagonists that are either made of those elements and/or are able to utilize them without any ill-effect to their being. If associated with malevolence, can go in line with Light Is Not Good-imagine sunburns, imagine merciless UV rays scorching everything they touch. Undead or demonic creatures have been depicted as being vulnerable to it, likely to its associations with light and fire. Due to its nature as an object that provides warmth and light, the sun has played symbolic and important roles throughout the history of fiction.