Merlin, Class Name Caster (キャスター), is a Caster-class Servant summoned by Ritsuka Fujimaru in the Grand Orders of Fate/Grand Order. She first appears as a combatant in Fate/Grand Order Arcade.

Originating from the Fate/Prototype worldline, she served Arthur Pendragon as his court magus. She is a woman compared to her male counterpart who serves Artoria Pendragon.

Another version of the Magus of Flowers, visiting from a different world. Always smiling regardless of the situation happening around her, she is a woman like beautiful flowers.

In front of her beauty, anyone would lose touch with reality and forget their hostility. On the other hand, her excessive beauty (and allure) make her a temptress that has a tendency to lead men astray. Though her calm demeanor gives the impression of a wise sage, her complete lack of tension and her emotionless way of thinking give the impression of a cold magus with no concern for the affairs of the human world.

"Now, now, no need to get all hot and bothered. No matter what happens, in the end you are all fleeting creatures, just like the birds. All's well that ends well, right? Ah, though I don't really want to see the end, or for things to go unfinished."

She describes herself an older sister, someone who watches over the masters journey. At the same time she is somewhat apathetic and comes of as seemingly uncaring.

She interprets everything objectively, and even when analyzing the ugliest parts of humanity, she describes them in a hopeful tone, saying "Not everything needs to be neat and clean. No matter how sullied you get, as long as you have one clean spot, a single shining star, that's more than enough."

She loves the human world, pranks, and boys.

The Mage of Flowers eludes practically all matters with an interested and amicable smile.

Unlike Man Merlin, she preserved her content mindset, never concerning herself with anything.

She's very aware of her status as a stranger to human society. She doesn't lament this fact at all, she just has "humans" and "me" split as two completely separate things in her head.

"I'm just something of a navigator tool created by humanity. I don't really wanna join the club."

"I'm just some woman wishing your journey would last forever. Well, I will pull some strings here and there if I ever feel like the journey is starting to get boring."

She considers Beast VI/S her irreconcilable archenemy.

(Source: TYPE-MOON Wiki)