Combine flour, 1 1/2 teaspoons salt, 1 teaspoon pepper, and cayenne in a large bowl.

Pat crab pieces dry and toss with flour mixture in batches. Remove excess flour.

Heat 3 inches of vegetable oil to 375°F in a wok or large pot.

Fry crab in batches until golden, about 5 minutes per batch. Drain on paper towels.

Fry chopped garlic in the same hot oil until golden brown, 2 to 3 minutes. Drain and set aside.

Bring a large pot of water to a boil. Add 1 tbsp. salt and spaghettini.

Cook spaghettini until tender, 5 to 10 minutes. Drain and toss with butter and half of the fried garlic.

Keep the noodles warm.

Heat 3 tbsp. oil in a wok over high heat. Add dried chiles and ginger. Cook until fragrant, about 30 seconds.

Add chopped green onions, serrano chiles, and remaining 1/2 tsp. salt. Cook until onions wilt, about 1 minute.

Add sake and cook until reduced by half.

Stir in fried crab and cover. Cook until crab is heated through, about 3 minutes.

Remove lid and cook until any liquid evaporates.

Stir in chopped basil, mint, cilantro, and remaining 1/2 tsp. pepper. Cook until herbs have wilted.

Stir in remaining fried garlic.

Transfer crab to a warm platter and serve hot with garlic noodles.