You can find Himeno's kit on the official NIKKE Twitter.
A review for Himeno will be released once we will actually be able to see her in action and test her ourselves. The first impressions are based solely on analyzing her skills.
We also enabled her skills on her profile, so you can check them there.
Weapon: Sniper Rifle
Burst Type: 2
Yes, Himeno is obtainable for free - we will get 1 copy of her from the collaboration login calendar and her dupes should be available from the event.
Skill 1 - Weak Spot Attack
■ Activates when hitting a target with Full Charge. Affects the target.
DEF ▼ 6.94% for 3 sec.
Since Himeno is a Sniper Rifle wielder, when you won't control her, she will always attack enemies with Full Charge. This means that in a boss scenario, you will be able to permanently keep it debuffed, but even in non-boss stages, this will allow the rest of your team to deal more damage.
Just keep in mind that DEF increase/decrease doesn't have that much impact on higher deficits.
Skill 2 - Invisible Hand
Cooldown - 20 seconds.
■ Affects all allies with sniper rifles.
ATK ▲ 10.98% for 10 sec.
Max Ammunition Capacity ▲ 2 round(s) for 10 sec.
A decent buff to Sniper Rifle allies, but sadly the values are a bit low, and also the cooldown is super long - 20 seconds. Dolla, for example, gives ATK buff to all allies on a 10-second cooldown, but I guess with Himeno being an SR rarity character they had to make it worse and not as universal.
The Max Ammo Capacity increase also helps with the DPS, but let's hope some weird ammo-related bugs won't reappear here (like it happened once already).
Burst Skill - Ghost
Cooldown - 20 seconds
■ Affects 1 ally unit(s) with the highest ATK.
Charge Damage ▲ 23.76% for 10 sec.
Critical Rate ▲ 16.35% for 10 sec.
The Burst gives a decent damage boost for your Burst III character (if she's an SR or RL wielder), but sadly it only affects one target. So the other 1 or 2 Burst III characters will sit through the Full Burst, twiddling their thumbs.
With Himeno being an SR rarity character tied to a limited event, we hoped that she would be at least as good as Neve, but sadly she looks pretty meh. I find it pretty ironic that she is only good in Sniper Rifle teams but neither Makima nor Power wield that weapon. While Himeno's Burst will help Power (since she uses a Rocket Launcher), her S2 will be useless for anyone who isn't using a Sniper Rifle.
Still, Himeno could potentially find a permanent spot in Alice's team (especially for Union Raid as there you actually need to prepare 3 teams) as she gives her everything she needs to become the best murder wabbit.
Overall, for new players that are starting their adventure with NIKKE, Himeno should be an okay addition to their roster (and team), but they will quickly drop her once they obtain a more universal Burst II character.