boundary / a bounded area or region / a bounded group of people, a society, a world as a social grouping, such as business, celebrities, or finance / the border edge of a thing

border, boundary, limits

natural / spontaneous

naturally / spontaneously / rarely / coincidentally

astonishing, marvelous, astounding, phenomenal, tremendous

first, initial / one-eyed

Kyūjitai form of 双方: both sides, both parties

Kyūjitai form of 双眼鏡 (“binoculars”)

Kyūjitai form of 双子: twins

Kyūjitai form of 双方向: two way, interactive