Smokescreen has been teaching his child how to fight and allows them to take part in the final battle; but the final battle is full of sadness.
Warning: Death

Smokescreen's P.O.V.
Much to the displeasure of the others, I have been training my child to fight with us. Ten years old isn't too young since my child is a hybrid. I still want to keep (him/her) safe. That doesn't mean I'm keeping them from fighting in battle, but I definitely will not allow (him/her) to fight Megatron. Even though (he/she) hasn't been to Cybertron; (C/N) wants to join the team in the final battle. Ratchet was able to build a custom battle suite for (him/her).

We are tasked with finding the star Sabor while the others fight the cons. Of course, it's on Megatron's war ship.
"Told you taking the phase shifter was a good idea," I smile and take (his/ her) wrist so we both phase into the ship. Most of the vehicons are off the ship, fighting.
Megatron didn't change the location where he keeps the artifacts. This is too easy.
"Now we can revive your homeworld, dad," C/N) smiles.
"Y-yeah."
This is something (Y/N) hoped would happen. She talked about taking our child to Cybertron while she was pregnant.
I wish you could be here (Y/N).

"Optimus! We have the star Sabor!" I yell as we run towards him.
"THAT IS MY STAR SABOR!" Megatron yells and Sims his weapon at us. I rush to get in front of (C/N).

(C/N)'s P.O.V.
I watch dad go down, and from the hole in his chassis, there's nothing Ratchet can do.
"Dad! Dad, get up!" I beg, even though I know dad is dying.
"I want you to t-to finish Megatron for me..."
His optics offline.
Anger and sadness fill me.
"I WILL KILL YOU, MEGATRON!"
I rush towards him with the star stabor.
"(C/N) NO!" Optimus yells, but I'm doing this.
"You're asking for your death wish, kid!" Megatron taunts.

Optimus Prime's P.O.V.
I can't believe we're watching this. It's too late to stop (her/him). We watch (C/N) stab Megatron resulting in him going out of Cybertron's atmosphere to float in space forever. Thinking Smokescreen's child died instantly, and pain-free doesn't help. Blood pours out of the suit and onto my servo.
"They're all together now in the AllSpark," I tell the others, but I don't think we'll ever get over this. A child died; a family gone. Even if Smokescreen could be repaired, I think we'd agree to let him be with his wife and child.

We decide to get (Y/N)'s casket and bury the family on Cybertron. Sadly, our other human friends' first trip to Cybertron is for a funeral.

The well of Sparks
"Where am I?" (C/N) asks, uncertain if anyone is around.
"You are in the well of Sparks," a voice replies.
"But I am half-human and have a heart."
"You are still my child. I am Primus."
(C/N) was taught about Primus; he's like the transforms God, but he's not considered a God.

The scenery changes to a beautiful field. (C/N) feels the green ground, puzzled.
"Grass?"
"Watching my children spend much time on Earth, I have enjoyed the beautiful scenery."
Primus disappears, leaving (C/N) uncertain of what to do.

"(C/N)!" (he/she) hears before seeing a human-sized figure and a transformer-sized figure.
"Mom? Dad?"
As they get closer to them, (C/N) smiles, "MOM! DAD!"
(C/N) runs to (his/her) mom's arms. The two hug as Smokescreen picks them up and holds them close to his chassis. (C/N) is sad they're dead but happy to be back with (his/her) dad and seeing (his/her) mom in person rather than pictures.

The three of them watch their friends. As (Y/N) has wished for ten years; Smokescreen and (C/N) wish they could communicate with their friends and be seen by them, then death wouldn't be so hard.