A study of Kit and Ty's runes: Pre-TWP (SOBH) vs TWP (pre-release)
(Last image from June 2025, I'll update as we get new art!)
Ty wears more useful runes to help with his training as a centurion, and some investigations and missions, whereas Kit uses more practical ones. I can imagine him using them for everyday things or to learn the basics of being a shadowhunter.
While in the snips from TWP, Ty we see he has fewer runes (I suppose the love one was added because it was for Pride, because it's used in weddings), and more basic and symbolic ones. For example, the insight helps the wearer better understand situations. It contrasts a lot with Kit, who uses runes for combat and some useful for missions: mnemosyne (for memory), protected and talent.
On the last art, Kit has the protected rune on his wrist. It's used to protect the mind against magical intrusions, like encantos. It's not difficult to imagine it may have something to do with the fey. And on his chest he has the talent rune, which is used as a "wish for greatness". In QOAAD, Ty drew it to Kit to help with his persuasive skills, but instead helped him unlock his magic. So I find it interesting that Kit uses it in SOBH and also in TWP (Moreover, they're different versions. It's strange because, as far as I know, there's no difference between them). What stands out to me is that Ty wears the insight rune not once, but twice, and in the same place.
But I think it may also be metaphorical, and more to do with their dynamic than the story. Ty is making an effort to understand Kit, while Kit is trying to be brave, but also protect himself, while he is hunted by his own memories.
We can see that the difference between SOBH and TWP is notable in Ty and Kit. Kit goes from more basic esporadic runes, to more advanced and combat-oriented ones, while Ty goes from more mental and skillful runes to simple ones. It's weird the difference in TWP between Ty and Kit. Maybe I'm reading too much into this, or maybe there's a reason inside the story.