You have to try really hard to make an ecchi manga that stands out, particularly if you were making one in the time before monster girls. This one...well, it certainly tried.
QWASER OF STIGMATA (Seikon no Qwaser), written by Hiroyuki Yoshino with art by Kenetsu Sato. First published in 2006 and first published in North America in 2010.
PLOT:
Tomo and Mayuri are two sisters who are left adrift after their uncle/guardian disappears. Their home is converted into a school dormitory shortly thereafter and the new dean's daughter has made it her mission to make the girls miserable. Mayuri gently accept their fate with the hope that someday things might get better, but Tomo is picking for a fight. They soon find an ally in the form of a strange Russian exchange student on the hunt for a legendary Orthodox icon hidden somewhere in the school. He and Tomo must somehow find a way to get along if they are to find the icon and protect it from those who want to use its power for harm.
