Please, you didn't even know whether Riven and Shyvana would make sense. Leave the lore-proving/disproving to me.
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Talon's not exactly adopted into the DuCoteau family so much as he was bested by General DuCouteau in combat. This one is not canon, nor is it anti-canon.
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They aren't blood sisters. Diana actually wasn't born into the Rakkor. Does Leona absolutely despise Diana over accounts of heresy and want to see her dead? Yes, absolutely. Anti-canon all the way.
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If they were both at an age to care about romance (technically, Amumu's ten or so) and Amumu wasn't undead, this wouldn't be so preposterous. Annie actually is friends with Amumu, but we know roughly nothing about that friendship other than her best friend is Tibbers. Yes, a demon teddy bear is favored over Amumu.
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You're incorrect about that, they actually are friends. They're both exiled yordle mages and only have each other (and Pix) for company so this ship has some canon backing to it.
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I'm guessing you're ignoring the canon Blitzcrank + Orianna one because you hate Blitzcrank? A lot of people do. And as much as Viktor needs some loving (preferrably in the form of a legendary skin), Viktor and Orianna are listed as rivals. We know about nothing of that rivalry, however.
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As Professer Lyte put it "Are you and Vi even friends? Seems tedious." Despite being listed as friends, Caitlyn's full respect for the law and Vi's vigilante attitude don't mesh well. That's probably why they have Jayce for neutral ground (he both respects the law and has attacked Viktor's fortress). Granted, they're friends, but they'd make for a lousy relationship.
DRAAAVEN!
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I actually saw someone pairing them and they had good logic. Now, they actually probably don't know eachother since they have no lore ties.
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Jarvan IV and Shyvana make the perfect couple! Both dead-serious, battle-hardened Demacian warriors who will gladly lay down their lives for their country. And J4 helped Shyv avenge the death of her father.
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Ok, the only backing this one has is that they're both cat-people. But they're also rivals, considering Rengar's a ruthless trophy hunter and Nidalee's a "protector", if you will, of the jungle.
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Garen Crownguard, Luxanna Crownguard. Most people don't know this, but they're actually siblings.
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These guys are more "accomplices in crime" than they are a romantic couple. In fact, nothing about either of them hints at romance except Twisted Fate did have an affair with Evelynn in times gone past.
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Both are Demacians and relentless hunters of all that is dark and malevolent, so this isn't too crazy. But from what I recall, they actually don't like eachother.
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or
Zed kinda toppled the Kinkou order so both Akali and Shen hate him for that.
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Riven actually killed the man Yasuo was supposed to protect and that eventually led to Yasuo having to kill his own brother. It's anti-canon, but the sodium content of Riven/Yasuo mains seems to back it up in game.
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Ha. This joke is older than the one about Graves cigar and has been disproven at least four times. There's a lot shoved into the lore that Ezreal is secretly dating Lux, actually.