The TYBW poems are a lot more...well, "concise" is probably the charitable way of putting it. They're not bad, but with a length limited to one or two lines, there's not a lot of room for depth.
Unless you're this poem, which is just beyond romantic to me. The obvious, literal angle is that it's about Masaki, who Isshin has related to the sun in the past, and how she burst into his life, and then how even after her infection with a hollow (the literal embodiment of sin), she still shone brighter than anything to him.
Conversely, you could take it to be by Masaki, and about Isshin, and how his love for her shone through his own sin, whether that be the offense to her heritage of him being a Soul Reaper, or offense to Soul Society of him giving up his powers to save her.
But really it's about both of them, and love in general. There's the love that you have when you first meet, the idealized love, where you're amazed that this person has arrived in your life. And there's the love that you have once you know that person intimately, up to and including everything wrong with them, all their negative traits, and love them regardless.
And there's a difference, but also, there really isn't.
