@Milanin both are technically correct. He's using the Japanese pronunciation of the English word "sun."
But still, since his in-game name is in romaji it should also be used for the translation in my opinion.
The curse is too much, regardless of how low the chance of encounter this is a bit much.
Most player will just remake their character if they have this kind of debuff, no wonder no player challenge the unique monsters.
I like how the manga didn't do some bullshit like "The MC beat the OP Legendary enemy on his first attempt because that's totally how video games work!" thing