A tale too stupid to be told

As an aspiring writer...well, now, there is a phrase that needs some explanation...some people write. They write a lot. they write very well. And, perhaps most important, they complete their writing.
Aspiring writers, on the other hand, may write a lot, they may write very well...in fact, often enough aspiring writers show flashes of brilliance that many true writers never show, albeit in short doses...well, aspiring writers simply never complete their projects. There is always something on the burner, never something in the editing room.
As an aspiring writer, I often have ideas I like. Such as this one.
I would like to tell the glorified, extremely violent story of an individual who is a fearsome fighter, virtually undefeatable in combat. However, he or she is tired of life and wants to end it. However, possibly due to an enchantment, he/she is unable to commit suicide or, in fact, in any way do anything less than their utmost to continue living.
The one "out" he has is death through combat. therefore he seeks out more and more impossible deeds. However, once engaged in combat, his self-preservation kicks in and he becomes an unstoppable force and emerges from the combat unscathed.
Naturally, in my best O Henry fashion, he would find some reason to love life. Paradoxically, this would turn him cautious in combat and lead to his defeat.
Of course, there are huge problems with this story. For instance, making a likable anti-hero/hero. Justifying his desire to die. Justifying his change of heart without the tired, trite love of another person. Oh, and...not aspiring to write it.