Let's Play Genius of Sappheiros (Extra) Part 32
5We fight another miscellaneous quest boss.
Elder Dragon:
Most painful boss I ever fought. It has high defenses and has no weaknesses (it is neutral to Holy). It packs a punch with both Physical and Magical attacks with two charge up moves that lead to Comet and Dragon Breath. Alice defending everyone will only help to a point. Aya can reflect breath attacks and Reimu can use barriers. That leaves only two slots left which one will probably be Byakuren or another buffer and one main attacker.
The wikia has some suggestions but I found none worked. I just stuck to my guns and relied on Alice's shields and hope for the best.
At 25%, the dragon may cast Elixir to heal himself for a great amount of health. If this happens, you may as well restart. Sakuya can use her field effect to prevent this heal though it will prevent your own heals as well.