Well Abel and Chrono has a horrible past that they are not proud of. The main character was once evil but turn to good, and they have a kick butt nun as a partner. They also join religious churches or organization. they also have an emeny from their past.

Both about Christianity versus Demonic Beings~ And both a slightly clumsy/cute demon with a mysterious past on their side.

Similar theme and extreme analogies between characters. Both circle around nuns who fight the evil with overgrown weapons and that are friends with a doomed vampiresque form of life.

Almost like twin series, both: + Heavily rely on religious themes and imagery, being about a pair's adventure on mission for the church; + Star a long-haired supernatural male lead, who's usually laid back and far trom threatening until he goes full power, and a nun as the co-protagonist; + Have non-modern and non-japanese settings, one in the 20's, the other futuristic (but also borrowing names of real historical figures); + Share similar humor, tropes and clichés alternating between battles against evil and moments full of drama; + Are early 2000's Gonzo productions developing in 24 episodes.

Both deal with religion Vs devil type stories. Both rock my socks!

Similarities between the 2 shows are pretty obvious : Chrono Crusade is about a demon, Chrono, and a nun, Rosette Christopher, working for a religious organization, fighting satanists involved in dark magic, and demons summoned by rituals. Trinity Blood involves a Crusnik (a "vampire to vampires"), priest Abel Nightroad, and a girl, Esther Blanchett, working for the Vatican to solve issues involving vampires. Even Rosette and Blanchett kind of share the same fate of becoming all so important somewhere in the story.

Both have religious themes. They deal with the church fighting against demons.

both series are about priests and vampires or demons who side with the church. both have main duo of nun & dorky fiend who seems ridiculous at first glance but is secretly a huge badass, and they are looking for someone very important.