To put it into perspective, "Zutto Zutto" translates to "Forever and Ever".
Innocence is Miku asking for everyone to try to get along without dragging real-world problems into the fun parts of Vocaloid, as well as an expression of gratitude for all the songs that people have made for her. It was written in the midst of a bitter three-way copyright dispute that was threatening to break the fandom apart. In other words, the writer was trying to stop a Flame War by reminding everyone about why they loved Vocaloid in the first place. D'awww.
The end of ''Rolling Girl'' by Hatsune Miku, which was about a girl who was implied to be bullied and her world was spinning wildly out of her control. In the fanmade PV, when she was about to end it, the boy who was with the whole time reached out and held her, telling her it was going to be okay now.
Regret Message, the third of the 'Of Evil' series, as well as Daughter of White, which is Regret Message from Yowane Haku's point of view.
Adding to this, there's Mothy's South North Story. Mind Screw aside, it's rather sweet when you consider the implications that the normal Rin has met the Rin from Story of Evil and appears to be trying to comfort her. D'awww.
In scissorsloid, Luka (at 3 minutes) is happy to see her "big sister Miku" visiting her room, and asks what she'll learn from her. She then proceeds to issue compliments that are very sweet, and she seems to really love and admire Miku, and it's an extremely heartwarming moment, especially because of the video's yandereness. That is, until she takes a knife and stabs her.
Reflection is absolutely sweet and it brings out those tears of happiness with just a bit of the bitterness.
"Cat Ears Switch", by Rin and Len. The little chiptune-y beat alone can give you the warm fuzzies.
Last Night Good Night is a heartwarming, happy-tear-jerking song about that feeling you get when you first feel love for someone, with an amazing video.
This rather suggestive video (NSFW) of Haku Yowane waking up in the morning following a night of passionate sex is one of very few moments of Haku experiencing genuine happiness.
Wrinkle... just Wrinkle... It's a perfect mix of loveliness and sadness
"Your Star" by Hatsune Miku. The sheer beauty and sadness of the song is what makes it so special.
GUMI's "Time-Warped After Chopping My Stag Beetle" is very weird at the beginning, exactly as the title sounds. However, at around three minutes, it takes a serious but uplifting turn. Gumi meets her future dying self, who tells her to live without regrets because she (in the future) doesn't want to be sad.
This relatively unknown little song called "Grave Visiting" (hakamairi) definately counts. It is about a little girl (Miku) who doesn't really understand why her parents visit the cemetery every summer with her. She keeps being bored and wants to go back home. Over the years she finally understands the meaning of those visits. In the second part of the song she is now an adult and still visits the cemetery every summer. She tells her grandfather how she fell in love with someone and got married and introduces her own child to her grandmother.
You people call yourself Vocaloid fans and yet you forget "Melt"?
KOKORO is a combination of Tear Jerker and CMoH. The fact that Len spent his life making a program that would allow Rin to able to feel human emotions is already sweet. The song that Rin sings for Len, thanking him for all he's done, is what really pushes things into Tear Jerker and Heartwarming territory, especially when that song was able to reach Len.
Miku's "1/6", in which she plays a girl with aspirations to become an astronaut and go up into space in a satellite. However, she decides to postpone those plans and give up the money she was saving up for them after she finds out that her boyfriend has been going through some major depression. She takes him to a pier where they go up a lighthouse, insisting that he needs to be "elevated" to cheer up. This works and he slowly begins to smile. All throughout the song she promises him that when she gets enough money she will take him to the satellite with her, where all of his sadness will melt away and only be 1/6 of his weight. Awww!
This video of Yuzuki Yukari confessing her feelings to a boy she likes. She feels disappointed when apparently the boy hesitates to respond, but then she gets a surprise when he grabs her hand and kisses her. The whole atmosphere (it takes place at a park, and at night) and Yukari's soft voice enhances the whole thing.
The ending of Elsetetra -The Witch of the Water Reflection-note In the video linked to here, the title is incorrectly translated as "Elsetetra -The Silver Witch-", but because "silver witch" is what the character is referred to once in the lyrics, this mistake isn't as serious as it would otherwise be.: When the title character is on the brink of despair after not having been able to prevent her love interest's death, her love interest's ghost shows up to comfort her.
Hello Again is heartwarming in that they can't understand eachother but nonetheless stay waiting for when they can.
This is sorta meta, but on Mitchie M's newest song, Viva Happy, the subtitles had some swearing, (or something) in them, and there was a very angry comment regarding it. Of course, the fandom being who they are, rushed to defend and swear at the person. Later, though, Mitchie M fixed it...
Mitchie M: Sorry for my wrong translation. I have changed it. I'm not good at English :-( Please get along with each other.
Youtube person: Mitchie M, dont worry about the subtitles, some people on internet over exaggerate things (and overreact).... luckily these people are the minority. Thank you very much for your consideration and for uploading this incredible and happy song! And for the few guys who are outraged by the letter song, I say one thing, "Viva Happy" =)
Rin and Len's Magic Mirror by Hitoshizuku x Yama is a mix of heartwarming and Tear Jerker. It's the story of a lonely young girl, a magician in a mirror who grants all of her wishes, and the friendship that ensues. It's adorable, and sad, and beautifully illustrated, and...heck, just watch it.
Half and Half, a Luo Tianyi song about familial love. The producer composed it as a birthday gift for their father.