Start with a clean and moisturised base
With Igari makeup being a minimalist look, you definitely want to bank on plump and smooth-looking skin to start off. J-beauty is quite simpler compared to K-beauty, and it usually puts emphasis on just three things: cleansing, moisturising, and packing on suncare (Japanese people love their sunscreens!). Making sure that you have these things on point before you start working on your actual base makeup significantly helps with that 'my skin but better' finish, considering that this look requires you to keep your foundation as light as possible.
(Photo from: Secondsacharm)
In contrast to Western makeup where everything is almost always full-coverage, J-beauty is all about keeping it sheer and dewy. However, compared to Korea's glass skin, which almost looks wet to the touch, Japan prefers the mochi skin trend where a velvety-looking finish is the most ideal.
To achieve this, use a thin layer of foundation (BB and CC creams are also preferable because of their skincare properties) to provide the lightest coverage, as well as balance the colour of your skin tone. While a second layer is not exactly recommended in order to prevent a thick and cakey look, make sure you buff your makeup completely before proceeding to the next step. Once you're done buffing, proceed to concealer.
Unlike Western makeup where it's all about drawing triangles under your eyes and using two shades of concealer for highlighting and correction, Japanese makeup is all about using concealers only for spot correction. This ensures that the thin and skin-like layer of the base is maintained, still allowing the skin to breathe and appear translucent. Cream concealers are also preferable given that they add extra dewiness to the base makeup's finish.
After this is done, dust the skin with the slightest amount of powder to set everything. In Japan, 'marshmallow' or 'mochi' powder formulations are quite common as they're not as heavy as Western powders and also have a slight sheen/mineral-like flecks of glitter on them to contribute to that glowy look.