History TearJerker / CodenameKidsNextDoor

** As Chad admits to being a FakeDefector and reveals what he had been doing while pretending to be a villain, he bitterly states that, in spite of learning his "betrayal" back in "Operation E.N.D." and wondering why he would turn on the KND, Nigel never once realized he had been faking it by helping him and Sector V in the sidelines, a revelation that briefly makes Nigel perplexed and unable to dispute. While Chad saying that is more due to jealously over Nigel being chosen over him as the Earth representative of the Galactic Kids Next Door, there's a sense of anger over Nigel automatically accepting him as a traitor without ever giving him the benefit of the doubt despite the close friendship they had and admiration Nigel had for him.

** Numbuh Five's BigShutUp to Numbuh Three when the latter bugs the former about what she wants for her upcoming birthday, and Numbuh Three is on the verge of tears--Numbuh Five ''does'' immediately regret it as she realizes how hurtful that was and apologizes to her.

--->'''Numbuh Five:''' My sister's a teen! The greatest Kids Next Door operative I ever knew is a teen! And I'll be a teen soon enough. I mean just look at me, I'm practically a teen now!

** For the entire episode, the two are at each other's throats. While Chad's reason for his belligerence isn't exactly clear until the finale, Nigel's reason is obvious: he wants to understand why one of his closest friends, a boy who had been mentor and ally to him, betrayed him and the KND -- a question Chad ''refuses'' to answer until his life is literally hanging in the balance. What doesn't help is that it seems Chad didn't care about all the people he hurt with his actions. Even learning the truth changes nothing in the end. While Chad wasn't a traitor, all of his genuine negative qualities have eroded whatever was left of Nigel's ideal image of him (especially since said qualities were the reason he (Chad) tried to ''kill'' him), and their relationship truly is unsalvageable.
* The ending of "Operation: I.N.T.E.R.V.I.E.W.S." Adding extra weight to it? It's the audience's goodbye as well. It's been a great six season run, and seeing it come to an end is just heartbreaking.

WesternAnimation/CodenameKidsNextDoor may be a kids show, but it can still be sad!

* The Galactic Kids Next Door teaser is full of this and NightmareFuel: Numbuh 1 is about to unleash ''something'' on Earth, which he says is infested with adults while Chad pleads with him not to, protesting that their families and friends are down there.

** Granted Numbuh 5 was just tricking Cree and Mushi did it on purpose, but it still hits home to anyone who feels stranded from their siblings despite having been close when they were kids.

* In earlier episodes, the whole process of [[LaserGuidedAmnesia decommissioning]] is glossed over. Then in the opening of "Operation: M.A.U.R.I.C.E.", we're introduced to an operative, Numbuh Nine, who's a good friend of Sector V. It's his thirteenth birthday and he's willingly going to be decommissioned. The combination of his speech, his screams while getting his memories wiped and walking out as a sullen teenager with no memories is pretty damn depressing even if it was all an act. And the Crowning Music of Sadness makes things even ''more'' emotional.
-->'''Maurice:''' So let me just thank each and every one of you... for the best years of my life!
** Decommissioning itself is a gloomy process. Imagine losing most of your memories from your childhood. Imagine forgetting your crushes and your best friends, and acting like they never existed.
** Numbuh Five's GrowingUpSucks speech from that episode.
--->'''Numbuh Five:''' My sister's a teen! The greatest Kids Next Door operative I ever knew is a teen! And I'll be a teen soon enough. I mean just look at me, I'm practically a teen now!
** It's also rather sad to see a flashback of Cree working with the Kids Next Door and seeing what a loyal member she was, before she became a teenager.
** Numbuh Five's BigShutUp to Numbuh Three when the latter bugs the former about what she wants for her upcoming birthday, and Numbuh Three is on the verge of tears--Numbuh Five ''does'' immediately regret it as she realizes how hurtful that was and apologizes to her.
* Vin Moosk's HeroicSacrifice at the end of "Operation: K.N.O.T.":
-->'''Numbuh Two:''' Who was that guy?\\
'''Numbuh One:''' ... A comrade.

* Operation K.A.S.T.L.E.: King Sandy torturing Rainbow Monkeys...and giving Numbuh 3 a ScarpiaUltimatum where he'll dip Rainbow Monkeys in nacho sauce if she doesn't agree to marry him.

* Lizzie's breakup with Nigel is unexpectedly serious. She recognizes that Nigel's duty to the Kids Next Door will never give her the boyfriend she wants and decides that breaking it off would be for the best. Might not drive someone to tears but it is a well-handled moment of drama that can inspire some empathy from the viewer. Worse, knowing what we know later about Lizzie, the whole thing might be a cruel charade.
** And at the very end, Numbuh 362 attempts to comfort Nigel by subtly asking him out, but he turns her down. Rachel is understanding, but you can clearly see the sadness and disappointment on her face as she leaves.

* In Operation C.A.R.A.M.E.L, we learn why Heinrich holds ill will towards Numbuh 5. 5 years, 5 months, and 5 days earlier an incident happened that gave Heinrich delicious caramel unknowingly at the cost of what he valued most. Turns out he used to be a female and she had lost what she had valued most, her beauty. Assuming Heinrich is 10 like Numbuh 5, this means Heinrich lost what he had valued most when he was only 4 or 5. At such a young age losing something that important to you would do severe psychological damage.
* Anyone else feel bad for the Chief Safety Bot in Operation S.A.F.E.T.Y.? WellIntentionedExtremist, yes, but it only wanted to make a world safe for kids. When it realized it had in fact hurt a child (thus paradoxically violating its programming), it realized since it was in fact a threat it must neutralize itself. [[VillainsDyingGrace After spiraling out of control, it pauses and says only "please get home safely" before it wraps everyone in bubble wrap and proceeds to blow up the space station, destroying itself and sending everyone back to earth unharmed.]]

* "Operation: O.O.M.P.P.A.H" Numbuh 1's father takes him on a fishing trip to bond. After a day of boredom and annoyance, Numbuh 1 snaps at his father and the camera pans up show his face (notable, as prior to this, it had been [[TheFaceless obscured]], so showing it swiftly shifts the mood) and he just looks heartbroken.
-->'''Monty Uno:''' I'm sorry, Nigel. I just wanted to be your friend.
** Then there's Nigel's reaction to his father's response. You can tell that he realized how horrible and ungrateful he must have sounded. It gets even worse when his father is kidnapped and he never got a chance to apologize. Just imagine the guilt he was feeling.

* Surprisingly, "Operation: A.F.L.O.A.T." manages to become a tad upsetting as it takes a turn towards ''Film/{{Jaws}}''-level territory as Sector V winds up being picked off one by one (except Number 4, who drowned in the asparagus sea), with it being played as seriously as possible given that the Jaws equivalent is a great white asparagus monster. And this is despite Stickybeard saving the day in the end.
* "Operation G.H.O.S.T." opens with the funeral of Chubbo, one of the KND's hamsters. Numbuh 3 is so heartbroken, and anyone who's lost a pet can relate.
--> "Goodbye, Chubbo. I love you."
* "Operation S.P.A.C.E", Mushi delivers a rather heartwarming speech about her sister when seeing Numbuh 5 and Cree fighting. Both look at each other for a moment.
-->'''Numbuh 5:''' W-What happened to us, Cree?\\
'''Cree:''' I-I-I... I-I don't know. I got older... Things change...\\
'''Numbuh 5:''' You know, when you were in the Kids Next Door, I wanted to be just like you. You were the best, and I was ''so proud'' to be your sister.
** Granted Numbuh 5 was just tricking Cree and Mushi did it on purpose, but it still hits home to anyone who feels stranded from their siblings despite having been close when they were kids.
** Somehow, Cree's insistence that she was going to do the same and Abigail was just faster sounds as if it's a lie and she was being ''sincere'' when lamenting that she isn't close to her sister anymore.
* In Operation S.N.O.W.I.N.G, Numbuh 1 ends up sick when it happens to be a snow day. The first time he’s seen in the episode is him sadly looking out the window and whining about how unfair it is. The fact he sounds close to crying just makes it all the more upsetting.
** Later on in the same episode, President Jimmy reveals to [[IgnoredEnamoredUnderling his secretary]] Anna that Lizzie is his "true beloved." Up until that point it was clear that she thought her romantic feelings for him were reciprocated, and her devastated expression as he [[ObliviousToLove unknowingly shatters her dreams]] is heartbreaking. At least they do get together by the end.
* Numbuh 362 explaining to Numbuh 1 why she wants to give up being Supreme Leader of the Kids Next Door. As she puts it, all she gets to do is file paperwork and keep millions of kids under control while said kids get to go on super fun missions and hang out in giant treehouses.
** [[Main/FridgeHorror Fridge Horror]] also sets in when you realise what Rachel had mentioned might have been implied to be one of the catalysts for Chad's/Numbuh 274's supposed FaceHeelTurn.
** Later in the episode, after Father is tagged, Numbuh 1 comes to talk to Numbuh 362 again, who has been crying over what she indirectly caused.
* A milder case, Operation C.L.U.E.S. has Mr. Sanban [[OcularGushers beginning to cry]] because he just wants his kids to get along.
--> '''Mr. Sanban:''' I just wanted my babies to be nice to each other! Is that so bad?! Is that so... ''wrong?!'' *InelegantBlubbering*

* ''WesternAnimation/OperationZERO''
** Numbuh One having a HeroicBSOD after he believes himself to be responsible for Grandfather's return.
** When, after getting to know the real Sector Z, they reverted back into their Delightful form.
--->"Tell the Kids Next Door we miss them!"
** Or later on, when we see Numbuh Zero once again as Numbuh One's BumblingDad, with no memories of being a KND operative.
---> '''Mr. Uno:''' I say, old bean! What are you up to? Making some more 2x4 technobob thingies?
---> '''Numbuh One:''' ''(hugs him, who hugs him back)'' No, Dad. I was just playing with an old friend.
** Every time Mr. Uno was ever saddened whenever Numbuh One angrily snaps and rejects a chance to spend time becomes HarsherInHindsight when one realizes Nigel's father is Numbuh Zero. You see in his days, Numbuh Zero and his brother didn't have such a happy childhood and lived under the (literally) tyrannical rule of Grandfather. In other words, Nigel doesn't know ''how good he has it'', growing up with a kindly, supportive father like Monty.
** Father's failed, rather deflated attempt at confronting Grandfather, if for no other reason than the fact that it's eerily reminiscent of RealLife abuse victims attempting to confront their abusers.
** Numbuh One being forced to fight his former teammates. Fortunately, Numbuh Two's birthday suits help turn them back to normal.
** Numbuh Five's heroic sacrifice.
** Numbuh Zero's final message to Numbuh One via the broken recommissioning module at the end of ''Operation Z.E.R.O.'' is both heartfelt and heartbreaking, saying that while he might not remember what he did, he wants to go on his greatest mission: being a father to his son.
---> '''Numbuh Zero:''' "Hello, son. If you are watching this, then we've won. Congratulations. I bet you're wondering why the Recommissioning Module broke. Well, I broke it. I had a hunch you'd want to get Numbuh Zero back. Well...look, I'd love to stay and have lots more adventures with the super cool Numbuh One and his team, but... I'm just not a kid anymore. I'm an adult. And I need to complete the most important mission of my life -- being a good father to my son. So, you're the keeper of the Book now, Nigel. That's right. Keep a stiff upper lip and make sure everyone gets to write their own crackerjack story."
** Zero and his wife do get recommissioned one last time, in the series finale... to say goodbye to his son, as Numbuh One leaves for the Galactic Kids Next Door.

* In Operation S.N.O.W.I.N.G, Numbuh 1 ends up sick when it happens to be a snow day. The first time he is seen in the episode is him sadly looking out the window and whining about how unfair it is. The fact he sounds close to crying just makes it all the more upsetting.

** After the arguments between the various aliens is silenced by whomever is in charge, they say it is his decision to make, one that is not to be made lightly. After a moment of hesitation, he makes a salute while stoically shedding a single tear and proceeding to activate the device.
** The only thing that makes Nigel pause and hesitate in the GKND teaser is Chad telling him that Abby would ''never'' let him do what he is doing. Nigel looks like he is [[HopeSpot going to change his mind for a split second,]] before the aliens in the GKND [[IgnoredEpiphany come in and ruin everything.]] The fact that he didn't even pause when Chad first mentioned Sector V's names says that he is already resigned to what is going to happen to them if he makes this choice.
** At the end, the watcher hears this from Abby; “Nigel Uno... ''what have you done''?”. It is clear that she is heartbroken. And we haven't even seen the reactions of Wally, Kuki, or Hoagie yet.

* In Operation S.N.O.W.I.N.G, Numbuh 1 ends up sick when it happens to be a snow day. The first time he is seen in the episode is him sadly looking out the window and whining about how unfair it. The fact he sounds close to crying just makes it all the more upsetting.

** [[Main/FridgeHorror Fridge Horror]] also sets in when you realise what Rachel had mentioned might have been implied to be one of the catalysts for Chad's/Numbuh 274's supposed FaceHeelTurn Face-Heel Turn.

--> '''Mr. Sanban:''' I just wanted my babies to be nice to eachother! Is that so bad?! Is that so... ''wrong?!'' *InelegantBlubbering*

** [[Main/FridgeHorror Fridge Horror]] also sets in when you realise what Rachel had mentioned might have been implied to be one of the catalysts for Chad's/Numbuh 274's [[spoiler: supposed]] [[Main/FaceHeelTurn Face-Heel Turn]].

--->'''Numbuh 5:''' But...\\

** The farewell between Nigel and Abby deserves special mention.
--->'''Numbuh 5:''' Look at you. Best operative on the planet. And to think I had to convince you not to quit this morning.\\

** Right before that, we have Numbuh 4 freaking out and [[CryCute crying]] upon seeing his baby brother Joey injured. Joey actually faked it using ketchup, but it can still strike a chord for some.

-->"Tell the Kids Next Door we miss them!"

--> '''Mr. Uno:''' I say, old bean! What are you up to? Making some more 2x4 technobob thingies?
--> '''Numbuh One:''' ''(hugs him, who hugs him back)'' No, Dad. I was just playing with an old friend.

--> '''Numbuh Zero:''' "Hello, son. If you are watching this, then we've won. Congratulations. I bet you're wondering why the Recommissioning Module broke. Well, I broke it. I had a hunch you'd want to get Numbuh Zero back. Well...look, I'd love to stay and have lots more adventures with the super cool Numbuh One and his team, but... I'm just not a kid anymore. I'm an adult. And I need to complete the most important mission of my life -- being a good father to my son. So, you're the keeper of the Book now, Nigel. That's right. Keep a stiff upper lip and make sure everyone gets to write their own crackerjack story."

-->'''Numbuh Five:''' My sister's a teen! The greatest Kids Next Door operative I ever knew is a teen! And I'll be a teen soon enough. I mean just look at me, I'm practically a teen now!

** The earlier scene: Throughout the episode, Numbuh Four showed frustration over trying to help Leona from the Delightful Children since they don't know her at all. Numbuh Five, sick of Numbuh Four's attitude, tells him in a ''rare'' sense of fury and anger, that the last time she didn't help a kid from the Delightful Children, they did [[NoodleIncident something to him]] [[ThisIsUnforgivable that she could never forgive]], which [[MyGreatestFailure lead to her stepping down as Sector V's leader]]. When Numbuh Four asks what was so bad, Numbuh One quietly says, [[WhamLine "They made me bald."]]

** For the entire episode, the two are at each other's throats. While Chad's reason for his belligerence isn't exactly clear until the finale, Nigel's reason is obvious: he wants to understand why one of his closest friends, a boy who had been mentor and ally to him, betrayed him and the KND -- a question Chad ''refuses'' to answer until his life is literally hanging in the balance. What doesn't help is that it seems Chad didn't care about all the people he hurt with his actions. Even learning the truth changes nothing, in the end. While Chad wasn't a traitor, all of his genuine negative qualities have eroded whatever was left of Nigel's ideal image of him (especially since said qualities were the reason he (Chad) tried to ''kill'' him), and their relationship truly is unsalvageable.

-->'''Numbuh Five:''' My sister's a teen! The greatest Kids Next Door operative I ever knew is a teen! And just look at me, I'm practically a teen now!

** [[Main/FridgeHorror Fridge Horror]] also sets in when you realise what Rachel had mentioned might have ben implied to be one of the catalysts for Chad's/Numbuh 274's [[spoiler: supposed]] [[Main/FaceHeelTurn Face-Heel Turn]].