What is the point of calling "Raichi!" by the King's side player in the original rules? Obviously to announce that the King can 'see' the edge of the board. This is equivalent to "Check!" in Chess.
But what's the point? The point must be that the defensive player is alerted to this possibility and must block it. At chess, the defensive must get out of check if he can. At BrainKing we don't play Raichi and if a defender fails to spot that the king can see the edge, the king's side will win on the next move. I think games that end like that are rather unsatisfying.
Therefore I propose the following small change to the BrainKing rules and implementation of Tablut:
If the king can see one edge, it is Raichi and the defender must try to block it if he can. The interface should not allow a non-blocking move. If he has no blocking moves then king's side wins straightaway;
If the king can see two edges, it is Tuichu and the king's side wins straightaway.
I think that would be much better. Please let me know your views.