びくともし
That is the correct spelling of the word "unperturbed" (unaffected, calm).
He doesn't seem unperturbed by the comment Eric made.
unfazed
Not to disturb someone or something
unperturbed
The boy was remarkably unperturbed by the terrible news.
The nasty argument left her unperturbed. (She was not bothered)
Despite the chaos around her, she remained unperturbed and continued to focus on her work.
Composed, undisturbed, unruffled, or placid. Those words mean unperturbed.
Self-confident would work. So would unperturbed. Source: The thesaurus.
calmtranquilplacidundisturbedunstirredcollectedserene
Undisturbed, calm and collected