Pretty much the entity of Chapter 5 combines this with Tear Jerker, but this moment takes the cake:
"Do your best," said Ferb. "And you need not forget me. It is good to remember the blessings of our past. You must try to put the bad things behind you, but never forget what you learned from them." Phineas looked at Ferb with pain, sorrow, and fear evident on his face. Ferb, despite the fact that he was a spirit, embraced his brother. Phineas wasn't sure how this was possible, but didn't really care. He hugged his beloved brother back.