(Youtube opening that can’t seem to be embedded here)
From the supernatural shonen manga (and one of my personal favourites), Ushio & Tora, Chapters 159 to 165 (in the context of the story arc spanning chapters 139 to 165)…
This is Kirio’s mother:
Or at least, that what he thinks.
The reality is, Kirio was kidnapped as a newborn baby by an avatar of the dreadful monster Hakumen no Mono (White Face, a nine-tailed fox-dragon bent on destroying the world one nation at a time for its own enjoyment) – who then posed as his mother, with the intent of training him to destroy its most feared weakness, the Beast Spear.
When said plan seemed to have succeeded, Kirio’s ‘mama’ reveals the horrible deception:
Kirio, of course, cannot believe it:
Well, push comes to shove, and the avatar’s plan doesn’t quite work out as planned. Protagonist Ushio recovers the Beast Spear and a trashing of the avatar and its flunky ensues:
But the wounded avatar has one more manipulation up its dark sleeves…
Kirio falls for it – perhaps out of desperation and confusion:
Meanwhile, the heartless avatar of the equally heartless Hakumen no Mono proceeds to attempt to incinerate the entire battlefield:
But you just can’t take some things too far over and over…
Is it… The end?
And here comes the tear jerker…
Poor, poor Kirio…
See also similar case of earning trust followed by betrayal from One Piece’s Kuro, chapter 34 (click for full sizes):
And other most tear jerker moment in One Piece IMHO, Luffy vs Usopp.