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Tear Jerker: Kodomo no Omocha
In Kodomo no Omocha, we have the revelation of Hayama's broken home life, and how Sana pulls a small Batman Gambit to help Natsumi and Fuyuki see how bad they're doing. It works so well that Natsumi breaks down crying, then speaks to Fuyuki about what has been going on, and soon they start doing better.
Don't forget Sana reuniting with her birth mother Keiko and meeting her half-sister Mariko. Even though Sana refuses to live with Keiko, she's still thankful for her birth and wishes her good luck as much as the situation allows.
This troper couldn't help but cry when Sana finally talks to Mama Misako after she met with Keiko. All this time Sana was afraid that her Mama would have given her back, but what she didn't realize was that Misako too had the same fear.
"I wanted her to know... That Sana...That Sana is my daughter."
Near the end of the manga when Akito breaks down crying over having to leave Sana for America and ultimately causes her to recover from the depression that had been causing her to lose expression in her face. I still cant read that scene without crying and its been four years.