If you're looking for manga similar to Sharin no Kuni, Himawari no Shoujo, you might like these titles.
Akira is a high school student. He belongs to an astronomy club and enjoys his school life with other members including Kotone. He loves her, but can't tell it to her. As summer comes closer, people around him fall in love with someone. What will happen to his love...?
Hoshiuta is set in the fictional town Mihoshi in Shizuoka Prefecture, Japan. The town is in a quiet, rural area on the west of the Izu Peninsula and borders the Suruga Bay. There is a high school named Mihoshi Academy in the town. The protagonist Kazuhiko Suoh and his friends are students of the school.
Rin, Nerine, Itsuki, and Mayumi find a strange watch that transports them back in time, where they met Forbesii before he is married and has Nerine. While he is engaged to Ai, his maid, Sage, is also in love with him, causing a love triangle.