If you're looking for manga similar to Happiness!, you might like these titles.
Melty Moment follows Takeru as he gets closer to several girls in high school. He ends up leading an election committee that is filled with cute girls. There's shy little Natsuki, serious little Misao, his childhood friend Yuuka, classmate Sumire, and talented Aoi. Who will he end up with?
One day, a weird girl with pink hair and green eyes appears in front of Nagi Tsukuba, an average high schooler. She claims to be Stra, the "Prophecies of Nostradamus" and after guessing his future and guess it, she starts living with him. What will happen with his school life...?
The story takes place in a city-state enclosed by the sea. Merchants and adventurers alike gather within the city known as the "world's treasure house". It is a city of endless possibilities and dreams. Here it is that the somewhat odd story of an adventuress and her happy-go-lucky friends unfolds.
The main male character is Asaba Yuma, and the story follows the school life he shares with many girls and his one male friend. These girls include Tsukishima Yuri and her twin sister Hanako, who is in the newspaper club, Yuma's little sister Konami, who likes shogi, and several others. Will Yuma find love in his teenage years?
Riki and his friends have been managing to form a complete team for the Little Busters baseball team and after overcoming some of its new members' internal conflicts, Riki and Rin slowly approach the "secret of this world." Will they be ready for the truth? In this world devoid of logic, something has started to move and soon will come the time when the lives of the Little Busters will change forever.