na-adjective
determined; single-minded; intent
Formal or literary term describing a state of being completely focused on one thing, often with a desperate or wild intensity. Similar to ひたすら but with a stronger, more emotional connotation.
See also: ひたすら
彼はひたぶるな思いで研究に打ち込んだ。
He devoted himself to his research with single-minded passion.
ひたぶるに
The sight of him running on desperately was striking.
ひたすら means 'earnestly' or 'with all one's heart' and is more common and neutral. ひたぶる is rarer and carries a nuance of desperate, almost wild determination.
The origin is uncertain. It may be related to the classical Japanese adjective ひたぶるし, meaning 'single-minded' or 'intense'. The kanji 一向 is an ateji assignment.