I've been thinking about this for a bit so here's a post about why Saint Traft and Rem Karolus is an awesome flavor win of a card.
So for this we're going to be looking at the tokens these two make. First, the 1/1 red human.
In the Planeswalker's Guide To Innistrad: Stensia, it was mentioned that Rem spent much of his time in the region. He only took orders from Thraben when he agreed with them, instead choosing to ride around on his horse Jedda and help the folks of Stensia.
Crimson Vow is the first time we see the 1/1 red human token in the precon. The woman depicted is also in the art for Stensia Uprising; she's on the right-hand side of the art.
Rem helped these people. He spent most of his career protecting them. Of course they'd come to his aid when he needed them.
Next, the spirit token.
The obvious bridge between the geist himself and the human who, funnily enough, refused to be bonded to a spirit during the Battle of Thraben in the Travails. The Order is essentially the only real Cathar force left, with Avacyn's church in shambles following the inquisition and the ousting of its Skirsdag infiltrators, like Jerren. Some spirits are still clearly willing to help to humans, as we saw in Midnight Hunt and Crimson Vow.
Finally, the angel.
Saint Traft was Beloved of Angels, and he was followed by an angel until his demise. Those he chose were also blessed by that angel. In Invocation of Saint Traft, we see the young girl he died rescuing taking up his mantle. (Many have said this art is Grete, but it's not. Notice her ring finger is missing the top knuckle -- the cultists who captured the little girl cut off her finger to taunt Traft. She later became a Cathar and was blessed by him.)
So the tokens are a really awesome, flavorful way to connect these characters. From the common man that Rem inspired to the angel that watched over Traft, the tokens are absolutely perfect for this team up.
