Note: Screenshots were taken while playing in the Japanese language on the worldwide Nintendo Switch version. It is the same game as far I know while in English except for localized name changes.
Developed by Tokyo RPG Factory and published by Square Enix, Ikenie to Yuki no Setsuna or localized as I Am Setsuna was released for the Playstation Vita in Japan on February 18, 2016 and subsequently for Japan and worldwide for Windows via Steam and PS4 on February 18, 2016 and July 19, 2016 respectively. It later became one of the launch titles for the Nintendo Switch worldwide on March 3, 2017.
A sacrifice to appease the fiend of the Island
The intro of the game from the official steam page:
“This is the story of Setsuna; a young woman of incredible inner strength and the sacrifice she must make to save the people of her land.
The Island had a custom.
To maintain peace, once a decade, a sacrifice was offered to a fiend on the island.
However, one year, the fiend grew violent before the next sacrifice was due.
Those living on the island were afraid and tried to calm the fiend by offering a sacrifice; Setsuna, chosen because of her powers of enchantment.
Setsuna must leave with her safeguards for the farthest land, where the ceremony of sacrifice will be held.
The taciturn masked hero of the story

The game offers dialogue choices throughout. Most choices do not make a major difference besides having a different dialogue outcome so feel free to answer however you choose. You are also free to rename any character in the game if you like, but I will refer to the characters as their official localized names.
Change of plans

Technical old-school RPG glory

Battles are done in turn-based fashion with Final Fantasy’s Active Time Battle (ATB) system being used to decide turn order. Like in Final Fantasy, you set either set it its traditional active setting or set it to wait in the options menu.
Battles feature up to three people at a time where each character has hit points and magic points above their ATB timer. The objective is naturally to defeat the enemy before it defeats you. The snowflake in a circle to the right of their magic points is something called your momentum gauge. After your ATB timer is full, it will slowly fill up and each time a little sparkle will be added to it.
When you have at least one and you perform a move, you will have a chance to enter momentum mode or singularity. If you press the indicated button just as you strike the enemy (the game gives the player a fairly adequate window to do this), a dialogue will show in the top-left indicating you have entered momentum mode. There are certain buffs that you can get during it. Here is an example below:

That’s the spiritnite

Flux capacity
In I Am Setsuna, there is something called fluxes which are just possible bonuses from talismans which can be adhered to Spiritnite. You have a certain chance after each battle to affix a flux. Each Spiritnite can have up to ten fluxes each but be careful as once one is attached, there is no undoing it. You will have to get a new Spiritnite if you want to change it (or just reset if you didn’t save). It is not absolutely necessary to do this in the game but it can make your party much stronger if you utilize them. There are plenty of possible combinations to experiment within the game.
Glistening in the snow

Winter Wonderland

Recipe for success

Watch for strong monsters
Special type of monsters called Spiritnite-eaten monsters appear in locations throughout the game usually in caves and such. These monsters tend to be very strong so be careful to avoid them when you first encounter them.