Also, I do remember that these events play a pivotal role in being w/Arshem:
-attempting to tell him the truth during the first battle
-needing to have an angel fish? (that yellow fish) or two, ready for him for the full confession/truth scene
-needing to have touched the Siren Globe in the Headmaster's office
-Affection being high enough for him to "save" you after the sparring scene
-winning the missing cat quest
And making sure to pick the highest affection related choices during times you talk to him on or outside of dates with him (usually choices that allow him to be himself).