I've tried everything it's just not unlockable yet
EDIT: I just realized that it might be added in the next update since the image is visible in the gallery under the lock instead of a black image under the lock like the other unobtainable ones
It is unlockable, if I remember right it's down the Good route, you need the goodness maxed out, then at the first gate when you need to give Gomamon your essence don't do so inside, you must do so outside, do this a few times and eventually it will unlock a blowjob scene, and you will also need to pullout here, angering Gomamon.
Next you need to just wait for a little bit click on empty space to pass time, but don't click any of the option boxes this will trigger a new scene where you go to sleep, and Gomamon sneaks into your pants to get your essence himself since you won't give it to him properly and this will be the Bodyjob scene.
Not sure why it's not working for you, I went in and tested this out on both the in browser player, and the download of the game, both worked going through the way I explained, I even tested if you need to try and save him or not, and both options still worked, I'll write out what I did in a bit more detail perhaps.
1: Play through the game being as nice to Gomamon, I didn't use dirty talk at all
2: Under Bonding I went through Petting, sexual belly rub, and then flirting, I used flirting multiple times until good was maxed out at the chains
3: Explore until you find the gate, one on of the explore options I carried him up the stairs
4: The Elecmon attack, seemingly doesn't matter if you try and save him or not, try to save him to keep goodness maxed out
5: Explore again and you will have the scene explaining essence
6: Bonding -> Sex -> Clawjob -> unload on his head
7: same as 6, Bonding -> Sex -> Clawjob -> unload on his head
8: Bonding -> Sex -> Blowjob -> cum outside
9: Now click on the empty dialog box to pass time with ... ... ... three or more times and wait briefly for the scene to start and that's the bodyjob scene started
this is what I just did and I typed this out while plaything through the first act again. Hopefully this helps you get it this time.
Uh I guess just make sure you are playing the most upto date version 0.76
Hey there. Someone already gave a very detailed explanation, so I hope you managed to get it. This scene can be missed if you are at the first firewall (after the Elecmon scene and then the drool scene that allows you the Clawjob) and then cum inside Gomamon in any way. You have to always pull out instead. Never inside, giving you the Blowjob option earlier and then screwing it up as well by cumming outside. It is a bit hidden in a way, but that is what makes it special. ^^