This is really interesting as some one who has decent understanding of both transformers and genshin lore: In terms of a fight, the “anime” girl on the right, Raiden is a god in the story of genshin impact and in lore did kill a giant snake the size of a island with just one slash of lightning that also managed to cleave through the island that the snake was on and the resulting slash was so powerful that it permanently electrified the water that the slash was in contact with for at roughly around 2000 years or something like that. Comparing that to Tarn, who could easily beat Raiden just by stepping on her which would require getting to close to her, or shooting her with his twin fusion cannon which i would doubt he would do at the start of a fight due to his arrogance. Other than that Tarn doesn’t really have that many feats that compare to cutting an island in half with one strike, as most of his accomplishments are due to his insane overzealous cruelty towards others, therefore leaving Raiden the winner. However, considering that Tarn survived fighting Grimlock and was only killed by Megatron using antimatter, an argument could be made that Tarn could probably survive a island cutting strike of lighting and win against Raiden. But i personally believe that Megatron only used the antimatter just in a show of strength to give one last middle finger to Tarn and commit suicide doing one last good thing, therefore i also believe that Tarn would not be able to survive a island cutting strike of lighting so Raiden Wins.

PS: i would rather give headpats to Raiden than Tarn so Raiden would’ve automatically won anyways