Kakeru Ozora is the tritagonist of Hearts in Ice. He is an astronomer who finds a piece of Princess Snow Kaguya's comet and takes it to study it further. He is part of a love chain, as he is in love with an astronaut named Himeko, but he is the love interest of Luna, herself the love interest of Artemis.
Kakeru carelessly rescues Luna from getting hit by a car by rolling into the street in the process, and he nurses her back to health. However, he himself becomes in bad health when the piece of the comet goes off, and somehow, because of different beliefs, clashes with Himeko.
(More will come.)