ひたすら
ひたすら · hitasura · JLPT N1 · adverb
earnestly
hitasura = 'only, nothing but' + 'earnest, single-minded': one thing done with all your effort, nothing else.
Root 'hitasu' (ひた) means single-mindedness, with nothing else mixed in. Use it for doing one thing nonstop or with total focus. Example: ひたすら歩く = walk nonstop.