[Unfortunately, Shun isn't the sort of person to smile and lie if it'll make someone less upset, so all he can really do is put that grounding pressure on her shoulder. Even though he still looks a little upset at Nanako's reaction, there's something resolved about his expression.]

Not everyone here has experience like I do. I can't fight all the time, but I can do as much as I can, and bring what only I can bring to our efforts here. [He lets out a short breath.] You're not the only one trying to look out for me. Even if I somehow take on too much, I won't be alone.

[However, there's an air to that which implies he doesn't actually believe he can take on "too much".]