N-S Crest is the 28th chapter of Doraemon manga.
Gian discovered about power of magnet, but Nobita humiliate him by saying everyone have known since kindergarten, so he was bowing his top and beating Nobita whenever he saw. Nobita asked Doraemon to help so he put out many crests and making an example by sticking "N" at Nobisuke Nobi and also "N" at Tamako Nobi, then Doraemon told mom that papa has called her; when she were near Nobisuke, she were bounced back and vice versa. Finally both are fishting so Doraemon replace the "S" at Nobisuke, so both of them are stuck together.
Doraemon stuck "S" on Nobita and Gian. When Suneo found Nobita he told Gian to beat up. Unfortunately Doraemon hadn't stuck the crest on Gian yet, but cut it fine. Gian wasn't able to beat Nobita up.
After that Nobita borrowed some crests and stick "N" on Shizuka; suddenly Gian threw lasso to pull Nobita, but failed. Then Nobita stuck the wrong crest and Shizuka was pushed. Nobita decided to change himself, but couldn't so he took off his shirt and stuck "N" at undershirt. Unfortunately, Gian was flung nearby so injured Gian and Nobita are stuck together.