This was a perfect shounen manga (for me). The motive of gabimaru fuel the main story, the mysteriousness of the unknown places ahead, the growth of every character, the struggle and complex emotion of sagiri.
The story also does not drag, does not filled with useless cliche nor does it repeat a tired formulation like some other (Samurai Deeper Kyo, Kenshin etc). The story too gets exponentially better towards the climax and every character had their satisfying conclusion (done well because usually it would be lame if execute improperly like some shoujo or shounen that goes full happy mode in the end).
The shinobi girl that looked up to gabimaru is among the best written albeit within short appearance time. A girl living her life in strife, falling in love with her companion (or her competitor though she forfeit her chance for him to be the only candidate). She and him both are destine to had no chance of loving each other (though she love him but sadly does not know how). In the end, the love is wrapped up in an abstract motive of (if i would not be able to get your heart while you are living, i would get it when you are dead)
This is symbolize by her eternal longing of to either want gabimaru to be the icy cold gabimaru, or to kill him of he strayed off. That twisted love is also concluded with the action of her stabbing him towards the heart (touching his heart, both literally and metaphor), him grabbing her hand, hug her and she finally reach the end of her life.
Despite she does not have gabimaru all the way to the end. She managed to receive it in a semblence form of an abstract love. She conclude it with a wish towards gabimaru to please let granted her this if she were to see him in another life, to which gabimaru fervently granted. She smiles happily (despite dying) and wishes him well for his future. Who knows perhaps in another life she would have the chance to get the normal love, if both turns out to live a normal life.
The final conclusion too do ended up rather well (some may say plot armor and so on but these people does not see it all to well).
The reason being, Rien is just another gabimaru. A person lost her one whole meaning of life, frantically searching for ways to get it back at whatever the cost.
The only difference being, rien held back the issue and lashing out at everyone else that is concern (Mei). Gabimaru on the other hand had a fervent companion that keeps his head straight while he move himself forward.
This is why Gabimaru is able to understand Rien in the end, and this is also why Rien finally understand and accept. They are both the same albeit walking in the opposite direction, she wishes to have hers while sacrificing everything while he wishes to have his while keeping his humanity intact. Hence, she decided to finally stop, reverting the injury she inflict on the present battle, and finally decide to join her dear husband in the afterlife.
A good twist, cliched done well, gary stu done well, and all. Deserving of the 10/10.