Fill a pot with ~1 inch of water and cover. Bring to a boil. Uncover, place a steamer basket in the pot. Place the eggs on the steamer. Cover again. Steam for 12 minutes.
While the eggs steam, prepare an ice bath by filling a bowl with ice and water. Transfer the eggs after they finish steaming to shock them and stop the cooking process. Leave them in the ice water for 15 minutes. Gently peel.
Separate the yolks and whites into different bowls. Mash the yolks until they become smooth. Mix in the Kewpie mayo, red onions, pickled celery, ground white pepper, kosher salt, smoked paprika, Dijon mustard, honey, lemon zest and lemon juice, and pickle brine, until the yolk mixture is nice and creamy.
Roughly chop the egg whites into at least pea-sized pieces. Fold the egg whites into the yolk mixture.
Scoop a nice mound of egg salad onto one of the bread slices. Gently press it down to fill out the slice, making sure to fill out every corner.. Top with the other slice. Cut in half, wiping your knife in between slices.