BkDk dating for about a year before Shoto goes up to them and...

There is *much* spluttering from BkDk before they both get out to do that they'd need to take Shoto out on some dates first.
(Meanwhile, BkDk are like: This is our chance??? We can seduce him into also being our boyfriend, romance, and spoil him so much that he's ruined for anyone else!)
(Oh man the "confession" that happens on their like 2nd anniversary where they all find out about the plotting.