Is there anyone in the Series, who can beat Reinhard in one on one battle?. His abilities, skills are crazy strong. especially His Divine Protection is a "CHEAT" Code , an extremely Overpowered. aint it?
Satella vs Reinhard would be an eternal battle, as they would fight forever.
However, in Arc 6 Ram stated that there are 3 others that come close to his level. The three are "Blue Lightning" also known as Cecilus Segmunt - "Admirer" also known as Halibel - "Crazed Prince" whoms name is currently unknown.
Arc 4 is fully fan translated, you can find it by just looking it up. Arc 5 is halway translated, as the translator stopped translating it. Arc 6 only have portions translated. The summary on Natsuki Subaru/Synopsis page is pretty accurate, so you can read that.
The Divine Protection of Sword Saint is the Divine Protection that the Sword Saint holds. The wishing for all divine protections is Reinhard's unique ability, none of the former Sword Saint had that power. By the way, it isn't called Divine Protection of Wish, that's just a fan name for his wishing ability.
Ram did say that there were three people who were on Reinhard's level, but that's just ignorance on her part. The basis for it was essentially that "Reinhard is the strongest in Lugunica," and likewise, "Cecilus is the strongest in Vollachia," "Halibel is the strongest in Kararagi," and "The Mad Prince is the strongest in Gusteko," so they're of similar status in the perspective of the world at large. The reality of it, though, is that Reinhard is more than just the strongest knight in his country--he's the strongest man ever born. The other three are more like Wilhelm, Theresia, Kurgan, etc. Actually, Reinhard wouldn't even be able to draw his sword against Halibel, according to the Oboreru trivia.