Here is the story and gameplay as I have it in mind presently (subject to change of course)...
1. On battle field. David has fallen, but gets up. Having lost his weapon he is battling to stay alive. He gets waved over by a messanger (Abishai, the warrior who saves him from the Giant by killing said giant.) Abashai sends him to speak with Commander Joab who orders David (albeit more of a suggestion since he is an advisor to the King) , “Never again will you go out with us to battle, so that the lamp of Israel will not be extinguished. (see 2Sam21:17b)”. Joab instead sends David to deliver supplies to Shimeah (David's brother) at the Outpost stationed just outside the Great Wall.
2. Upon taking the supplies to Shimeah and recruiting him to fight alongside him, David learns that Shimeah's son Yohnathan (David's nephew) would also be a great fighter, but has been hiding away at the Oasis.
3. Yohanthan and David must dual in an effort to prove his ability to fight.... (some clever storyline to come up - as either party could instigate the dual.)
4. Upon Recruiting Yohanathan David learns he has been fighting along with great mercenary warriors, Sibbekai and Elahnan, who are camped out in the Cave of Wonders. They are known as "The Crystal Outlaws" and for the right price will aide you in your quest.
5. David is sent to collect collect crystals from loot points scattered around the map and after collecting enough for payment he is able to hire the "The Crystal Outlaws"
6. Everyone has their business to attend to... David learns that his brother Shimeah had died to Raphachik (un-named in scripture, here meaning 'little Rapha') in battle. Yohnathan, David, Abashai, Elhanan, and Sibbekai all return to the battle field to fight the giants of Rapha- Ishbi-Benob, Saph, Lahmi (Goliathh's Brother), and Raphachik. David is offered a place to fight alongside and be known as one of the greatest warriors - A Crystal Outlaw.
2Samuel 21: 22 "These four were descendants of Rapha in Gath, and they fell at the hands of David and his men."
7. In a final scene (perhaps in a public award ceremony perhaps?) , Joab commends the 5 warriors. and gives a speech that though they may be considered Outlaws in a world fighting against them to never lose hope or faith in God for he is our salvation. There will one day come a King - like David - who will be a Messiah for all eternity - one who will reign forever on the Throne of all People, The Throne of all Warriors, and The Throne of all Crystal Outlaws. (and then gives them a medal or something.) roll credits.