The Promise / Serah's Theme Tab par Nobuo Uematsu

Final Fantasy XIII-The Promise/Serah's Theme

a|-7--8--7--5--3----|-3--1--0-----0--|---------3--0-----|--------3-----|
e|----------------1-|----------3-----|---0--1-----------|---0--1----3--|
c|------------------|----------------|-2-------------0--|-2------------|
g|------------------|----------------|------------------|--------------|

a|-7--8--7--5--3----|-3--1--0-----0--|---------3--0-----|---------------|
e|----------------1-|----------3-----|---0--1-----------|---------------|
c|------------------|----------------|-2-------------0--|---2-----------|
g|------------------|----------------|------------------|---------------|

a|-8---7--5--3------|-8---7--8--10--3--|-12---10--8--7--|-5--7--8------10--12-|
e|---------------1--|------------------|----------------|---------------------|
c|------------------|------------------|----------------|---------------------|
g|------------------|------------------|----------------|---------------------|

Repeat ad nauseum 

-OPTIONAL- End/Transition
a|-10\8-8/10-10/12--|
e|------------------|
c|------------------|
g|------------------|
(Some versions of the song that I listen to have a transition, so this is optional. I noticed that it works alright as an ending too. If it doesn't work for you, you can just let the last last note [Fret 12, String a] ring.)