in Russia we don’t call them “Viktor” and “Yuri”
we call Viktor “Vitya”, “Viten’ka”, “Vityok”
and we call Yuri “Yura”, “Yurka”, “Yurochka”
all of this is diminutives, “Vitya” and “Yura” it’s casual, “Viten’ka” and “Yurochka” it’s gentle and fluffy and “Vityok” and “Yurka” it’s kinda familiarly
maybe this info would be useful for ficwriters idk