Hearts In Ice is the secondary protagonist of "Sailor Moon S: the Movie" (originally named Kakeru Ozora). He is a brilliant astronomer who nevertheless believes in the Japanese legend of the Bamboo Cutter. He never tried becoming an astronaut after he got rejected on his first try. His obsession with the legend's Princess Kaguya is why he studies the moon. He finds a shard of Princess Snow Kaguya's comet in ice and keeps it in his observatory
What makes him count as a hero is that he saves Luna (who, developing a cold, collapses crossing the road) from getting run over and nurses her back to health. She develops romantic feelings for him and even kisses him in his sleep. She feels that her love is unrequited when she finds out his love interest is an astronaut named Himeko Nayotake.