On paper, it doesn't seem like there'd be a lot of crossover between the Dark Souls and Kingdom Hearts fandoms, but the internet is a strange place in 2020, and now there's a mod that lets you play as Kairi from Kingdom Hearts 3 in Dark Souls III, with the character 'worn' as a kind of costume.
The mod swaps out the knight armour set with components of a Kairi model, so you'll have to be wearing the complete collection of knight gear for the effect to work - that's not all that tough to get your hands on, since you'll start out with it if you play as a knight. However, the mod also replaces the 'young' voice for female characters with Kairi's sound effects, so you'll also get her voice lines in the game if you have or build a character with those attributes.
But wait, there's more. This mod also includes two versions of the trademark Kingdom Hearts Destiny's Embrace keyblade, which take the place of two Dark Souls 3 weapons. For Destiny's Embrace (Attack Form), you'll need to equip a normal longsword, and for Destiny's Embrace (Magic Form), equip the Cleric's Candlestick. The longsword is another easy item to find, but for the Cleric's Candlestick, you'll need to defeat the Deacons of the Deep, found in the Cathedral of the Deep, and then transpose their soul to create the hybrid weapon.
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