not to gintama on main (a third time,baby!) but it should be pointed out that the reason Kintoki couldn't predict that Gin would willingly die to protect his loved ones, despite that cliche being incredibly common for protagonists, is because Kin saw the role of Main Character as a privileged position while Gin recognizes it as a responsibility.
Throughout Gintama Gin doesn't get to enjoy many power fantasy protagonist privileges, even in a meta way. There are hundreds of chapters where the main punchline is his misfortune, and not even in a way that makes the reader sympathetic to him.
His trademark protagonist kindness, often used in shonen to give the protagonist rewards for basic human decency, is instead taken advantage of in many comedic chapters (he didn't HAVE to install that ghost girl into his scooter, you know) and gets him no kindness in retyrn most of the time.
His cool backstory? The thing that usually gets a character sympathy from other characters? Even by the end of the series i don't think even Shinpachi knows Gin was the one who killed Shoyo. Fans bring up the "unutilized shipping potential" of Gin bonding with Tsuki over their similar pain, but i don't think a Gintoki who willingly shares such a personal pain would truly be the same character anymore.
Harem? Nope.
Heck, Gin doesn't even get his own special shonen attacks.
