Clash of Diana and the Solari

Certainly, the world will plunge into darkness if the sun were to disappear. However, the Moon also brings a bit of light during the darkness. Diana isn't opposed to light, she just thinks that Moon should be the only light source because she got betrayed by the Sun (or their followers). Her goal is to ensure the Moon is the sole source of light that is worshipped, and the Sun can just take a hike because based on personal experience, it's a sack of hypocrisies and lies.

Like for this instance, there is no way Diana would associate herself with Nocturne who wants just mere darkness, no moon to shine on.

Though there is a tragic thing on this. Diana is so consumed in her anger that she forgot an important detail: Where does the moon usually get the light to shine on the night? Sun. How Diana could think that Moon is a source of light by itself, I do not know. But this journey can only end with Diana going "Okay... now the Sun is gone, so Moon! Why aren't you shining!? Wait, is it because I just destroyed your source of warm light, the Sun!? NOOOOOOOO!!!!"

Also somehow, this kinda seeps into this particular stuff about her joke:

"A man, a woman, and a yordle walk into the sun... They die! Because it burns them alive? Heh heh heh..."

This joke can be seen in a way to demean the sun further, because she thinks that's all it's good for: Burning people alive.

The Solari have barely any history so who is to say sending an assassin would be beyond them? Additionally, Diana is never mentioned in Leona's lore and vice versa, there's nothing to indicate this is a personal feud other than them both being the sole representations of their respective factions. And in what situation is an assassin's task ever cut-and-dry as in "I know exactly where my target is and I'm going to their doorstep and this is going to be a breeze, easiest job ever" never, an assassin's job is to hunt.

We know the Solari, pre present-day and post-purge, as a religious organisation which exists in one of the most remote regions of all Valoran. Certainly they were aggressive and in no way beyond brutal violence during their conflict with the Lunari but what enemies might they have had after the defeat of their sole enemies in the world? Certainly speculating they have never made use of assassins in that period is a gross generalisation, I will admit that, but there simultaneously is no evidence of any sort of foe they might have needed to send them against.

Diana is never mentioned in Leona's lore for two very obvious reasons. Firstly because Leona's bio entirely pertains to her ascension and arrival at the Solari compound and secondly because Diana was just another face among the Solari until some time after Leona left for the League (And still in very early concept stages at that point). All talk of connections between the pair, which makes up a huge part of why most people are invested in the story, has come from discussions with Rioters at various times following Diana's announcement. The relationship between the pair before Leona left for the League, and indeed the nature of that relationship, is a massive point of discussion.

To give you the old IronStylus quotation: "We want them to be intertwined, and without delving too far into assumptions and implications, without getting too detailed about their past relationship, what is more tragic than to have to kill someone that you love?"

*As a Solari acolyte, Diana admired Leona a great deal from afar. Before becoming the Chosen of the Moon and learning everything about the corruption in the Solari, she saw Leona as the ultimate good, a valiant protector. A small amount of that trust and longing for acceptance would remain. *- Riot Runaan

How does one rebuild an order alone? What is a religion without a following? The journey to reinstate this long-lost faith would be pointless without those to preach to. And those that discover truth NEVER keep it to themselves, so why would Diana choose to carry out this mission alone? Nowhere does it state that her goal to enlighten is solely meant for the Solari, she says all her "foes" (whom ever that may be) will either revere the moon or die by her blade. This leaves room for her, if she so chooses, to expand her potential influence beyond Mt. Targon and to the rest of the Rakkor[.]

"Right now, being as used to solitude and isolation as she is, the idea of building a cult following doesn't quite occur to her--she's devoting herself to finding and executing the rest of the corrupt Solari (and, of course, Leona)." * - RiotRunaan * As for what Diana would do should she succeed at eradicating the Solari... I think there's an element of her tragic story here. She's given herself a very singular and fatalist purpose, and I don't believe she's ever allowed herself to stop and think about the end-game... and if she has, she doesn't have a very... positive view of her ongoing role in the world once her mission is complete. More food for thought. - RiotRunaan

Diana is an iconoclast not someone seeking to build a new institution. Her sole purpose in the present day is the destruction, and/or forced conversion, of all those who would stand against her and the truth she embodies, and she brings the truth to others at the tip of a blade rather than silver-tongued sermons meant to sway hearts and minds. Diana has "learned to be solitary", to quote Runaan, and thus she works alone with no eye to allies.

If, like you said, Diana had no interest in taking the role of preacher, having Elise delegated to spread the word would not be far-fetched. Before allies are allies they are strangers no? They don't need a long history to become counterparts. The alliance would benefit both in the terms that Diana would have Elise's following to start with and Elise would have new territory and new victims that she wouldn't have to convert to devour. While this part is a bit of a stretch, its not implausible whatsoever.

I think it's a little implausible for Elise to see the worth in seeking out a semi-legendary figure somewhere in the wilds of Mount Targon purely for the purposes of expanding an operation she seems to be fully capable of managing alone, particularly when one considers that she desires victims she can expedite to the Shadow Isles. By aligning herself with Diana, Elise would be committing herself to a region which is just about as far away from the Isles as anywhere else in Runeterra and already has something of an established cult in the Solari.

Beyond that, as covered in the previous post, Diana is a solitary creature and has little reason to trust anyone else at all. She's known little else beyond lies and betrayal, perceived or real, throughout her whole existence and only now has the power to realise her goals alone. Why would she trust in someone else to preach her goals, particularly someone like Elise whose agenda revolves around spiriting their new converts away rather than solidifying a new power base?

Unsure what you're saying here

The conflict is currently Diana vs the Solari (Essentially Leona).

You're proposing Diana, Elise and Noxus versus Leona and the Solari, the Rakkor and Demacia. It's a completely different scale of conflict which would only serve to distract from the original elements and ideas by introducing a cornucopia of new characters and agendas to the mix. Where is the purity of the original conflict when it's now being fought for political reasons by individuals who have absolutely no interest in the solar and lunar cults?