I'd say Sebastián is based on Raum, at least in the anime. I haven't read the manga. We see him take the form of a crow a few times, which is somewhat of a giveaway, but he also has other characteristics of Raum. Another clue is that he used a tetragrammaton - talisman for love; one of the Lesser Keys of Solomon in which Raum as listed as one of the 72 demons. Raum is able to invoke love as one his powers. The fact that he is also an Earl of Hell is just a lovely irony. On a side note, I believe that Claude Faustus is Tsuchigumo, a Japanese spider demon. Since they don't come from the same mythology one way to determine the stronger would be a sort of race, which makes that series a little more fun.