OMG HI HUA!!! YESS I HAVE SO MANY THOUGHTS ABOUT THEM, he feels similar to an extent with Kafka with his power granted by Xipe.
His demeanor is much more calmer and his preference for violence low, with most if not all possible work to be done so via manipulation.
While Kafka and Samfly have a direct and violent approach which is beneficial for Blade who has no qualms about combat and it's consequences, him working with Sunday would be SO INTERESTING.
Sunday would not hesitate to use Blade's disposable and reusable nature against whatever the script demands, but his preference for peaceful missions might actually benefit Blade to the point he actively seeks danger.
Also with reference to all Sunday's religious imagery isn't it fun to think of Sunday being the one to offer a sacrifice via Blade for every mission? (Sunday always had himself on the line in achieving his paradise and goal, he was the greatest sacrificial lamb, yet now here he is letting Blade get killed or killing him to create stepping stones to fulfill a script that will lead him to paradise)
I just love to think of how of all the people Sunday might actually prefer the company of Blade the most with his simple dream of an end and his own of a paradise