Arlecchino, Penguins, and Angels
This theory has a bit of everything.
Naming Parallels
Perinheri- the in-game book confirmed to be related to Arlecchino's past by her 5th character story
Peruere- her birth name
Pers- Freminet's pet penguin's namesake, readable as the in-game book Tales of a Snow-winged Goose. This is based on Mother Goose from our world, which has a harlequin variant. This book also includes a story about a "Princess Marcotte" who is clearly meant to be Clervie.
Le Père- the French word for father
Male penguins- that is to say, father penguins- famously go great lengths for their children.
The Chinese word for penguin includes the word for goose
Hleobranto Innamorato & Blade Runner
Hleobranto Innamorato is the other name for the book Perinheri, and seems to be based on our world's Orlando Innamorato and Orlando Furioso books. In volume two of Perinheri, we hear about Hleobrant and his unrequited love for Angelica, which parallels our Orlando books.
This is further corroborated by the local legend Fairy Knight Twins, Angelica and Medoro. In our Orlando, Medoro is the man Angelica ends up with. The achievement for defeating them is called "Tears in the Rain", a reference to the Blade Runner monologue that is repeated in Tales of a Snow-winged Goose with the line "from red giants to white dwarfs, from the shoulder of Orion to the glimmering Tannhauser Gate..."
The central theme of Blade Runner is the divide between the humans and the replicants, something paralleled in Perinheri and Tales of a Snow-winged Goose. In Perinheri, it says that the Crimson Moon dynasty existed before birds split into domestic and wild kindred, and Tales of a Snow-winged Goose says that seagulls split into two races; seagulls, which continue to fly; and auks, which would never take to the skies again. Clearly, the metaphor here is that humans have split into two races.
It wasn't until I watched this video that I began to understand what these parallels might mean for the overarching storyline. Crucially, the replicants are soldiers for an interstellar war designed so that humans don't have to fight.
Angels & Seelies
This is Arlecchino's boss form. Typically, she has just half a wing, but here, she has six. I most frequently see this design being likened to the appearance of a spider (which would match visually with the Black Widow), but I see this has the six wings of a seraph. In Judaism, seraphim are angels associated with fire, constantly burning; seraph means both "burning" and "serpent".
I don't think it's a stretch at this point to say that Seelies are angels. In fact, there are measures to prevent Seelies from falling in love (and having offspring) with humans- why would this be? Perhaps to avoid creating a Nephil, as might happen according the Book of Enoch (which Genshin takes inspiration from). The Earth is understood in Jubilees and Enoch to have been flooded, inp part, for the sins of the Nephilim, which included drinking blood.
Kaeya & the Blessing of the Crimson Moon
Arlecchino can use the blessing of the Crimson Moon's blood, probably due to her lineage. The same goes for Kaeya, who, like Arlecchino, isn't effected by the "curse of wilderness" which Chlothar says turns all but pure-blooded Khaenri'ahns into monsters.
If you read the lore for Arlecchino's weapon, the Crimson Moon Semblance, you will understand the connection. The drinking of wine symbolises receiving the blood, and the blessing, of the Crimson Moon. How does this connect to Kaeya? Recall his father's letter from Hidden Strife. The Alberich clan are connected to the concept of purifying flame, the same concept as purgatory.
The Wagner Section
For me, every great Genshin Impact theory needs a reference to the operas of Wagner. In this case, it's the "Tannhauser gate" line in the Blade Runner monologue, a possible reference to Tannhäuser, the opera. It follows a bard of sorts and his infatuation with Venus and her underground realm "Venusberg". The evening star in our world is in fact not a star at all, but the planet Venus, and is associated with the fallen angel Lucifer (the demon to which the Ars Goetia's Paimon is obedient to). Khaenri'ah, the underground nation with its star motif, seems to reference Venusberg.
