This is both a simple and difficult question, as the Xbox brand has never been particularly popular in Japan for various reasons. As such I feel a focus on niche titles may be the best bet, essentially with Sony's shift to a more Western brand including moving the HQ to California, try to use the money from said check to outreach to smaller developers and various AA teams. Nippon Ichi Studios is in a bad spot right now but has some solid IPs people adore, so it'd certainly be doable to give them the cash they need to finish the new Coven of Dusk sequel and as a stipulation make it an Xbox One timed exclusive, possibly revive some older IPs like Soul Nomad as exclusives.
NIS, Idea Factory, companies like these give a decent niche to their competition so funding them to make Xbox exclusives would help a lot towards increasing brand adoption and retention and aren't so big that they wouldn't care about financial assistance. Get some new studios based in Japan through that Xbox Japan branch to make more bizzare and experimental stuff like what the original Xbox and early 360 had. Maybe even try to get Marvelous to switch development of Senran Kagura 7Even from Playstation to Xbox if the creator is willing to return to working on it, then he could make the game he wanted as an Xbox exclusive and a brand like SK would bring in plenty of people if Playstation simply wasn't an option.
Outreach and expand, convince developers that you want to see their visions come to life unhindered and the gamers will come along for the ride.
Also avoid canceling anything because it probably hurt their rep when Scalebound fell apart.