How does Trinity Blood end?

Answer 1

Abel is ressurected through what ever Lady Katarina told Tres to pour in Abels coffin. Cain shows up to the show as Abel becomes concious and they go in a battle. It is unclear who won how ever they do give clues. On abels body you can see similarities between what Cain used to look like so in short Cain completed his objective to absorb abel inside him and their bodies became one.

Answer 2

Most anime series will be open-ended in the hopes that it will generate enough interest for a continuation of the series due to popularity and public demand .