Both Battle Network and the Boktai games have been doing cross-cameos with each other for some time. In Battle Network 4, the player can meet Solar Boy Django during the game and perform a side quest with his help, and various Battle Network games feature GunDelSol chips and other cameos.
I haven’t played the Boktai games, but I know at least one of them involves some cameos of Battle Network as well, such as a special mini-game of sorts where a player using one game can fight a battle with someone using the other.
Thanks to MegaMet for the screen shot.