Narsil will have a long and glorious history, and we are now putting a bit more of that together. Surprisingly, the fate of Narsil came up in Session 5-29 while speaking about the culture of the Edain. While there has always been a temptation to make Narsil someone's 'second best sword', the only place we want that to happen in our story is while Túrin is living in Brethil. Túrin's choice of Gurthang over the available Narsil will be of interest to our story-telling.
And so, here is the history:
1) Season 4 - Narsil is forged by Telchar. Narsil is commissioned by Maedhros as a gift for Aegnor, whose sword broke in the Dagor Aglareb.
2) Season 5 - After Aegnor's death in the Dagor Braggolach, Finrod will gift this sword to Andreth, in memory of his brother.
3) Andreth will join the refugees from Dorthonion in Brethil. The sword will become a treasured heirloom among the Haladin.
4) Narsil will make its way to the Havens by the end of the First Age.
5) During the Third Kinslaying, Maedhros will recognize Narsil and pick it up as spoils from the battle. His brother Maglor will pick up a young Elrond and Elros.
6) Elrond will be gifted Narsil by Maedhros at some time before the end of the War of Wrath. Narsil will be Elrond's sword while he serves as Gil-galad's herald.
7) At some point during the Second Age, Elrond will gift Narsil to a Numenorean who aids the Elves in their battles in Middle-earth against Sauron. This individual will either be a Lord of Andúnië, or their descendants will be. Narsil becomes the sword of the Faithful.
8) Amandil will gift Narsil to Elendil prior to the drowning of Númenor.
...and we know the rest from there.
Obviously, there were a few pitfalls to avoid with the history of Narsil. One, is that we did not want it to merely be an 'heirloom' for thousands of years and not take part in the story in any way. There has been a strong desire to avoid making it 'Elros' second-best sword', as we know Aranruth is the sword of the King of Numenor. Another is that we did not want Narsil to be used in any Kinslayings, nor to have any kind of tainted history the way Gurthang does. And thirdly, we wanted the history of Narsil to be very much tied up in the story of the Edain and the Númenoreans - this sword, though made by a dwarf early in the First Age, becomes an heirloom and symbol among Men. It is borne by Elves, but it is not only an Elvish weapon. There's room for 'filling out' some stories (for instance, between 3-4), of how a Lord of Brethil takes up Narsil for some reason (perhaps the Nirnaeth Arnoediad).