Shinkai Shoujo

Hikari Tanaka was rescued from the ocean floor a year after disappearing at sea by the Deep-Sea King, returning with abilities tied to deep-sea creatures. Her childhood friend Yamada is overjoyed to see her but notices unusual traits, such as her body glowing and becoming see-through. Despite these oddities, Yamada, who cares for Hikari, makes an effort to adjust to her new condition, though challenges remain.