https://youtu.be/vCEmTbdVr6Y?t=15m54s {Time Stamped}

There's no such thing as a bad hero in King's Raid. That being said, there are some units who do very well in PVP and some units that need a lot of synergy to work. Without someone like pull units together, Reina isn't going to do much. Epis, however, will.

Me(~low masters) and a few challenger players were talking last night about Epis and the meta. Epis is actually a fairly dominant force that a lot of people are sleeping on. Just take your gear from Rrina and slap it on Epis. :D

Now, if you want to make Reina work in PVP you need to think of her as a late game clean-up. She has the ability to dodge a lot of powerful abilities. She's an amazing force vs baud/leo teams that don't run Nyx as they generally don't run a tank. EG: Baud/leo/arch/Luna you can just save mana for Carrot + Arbiter, pop your 1 to dodge all of their damage then proceed to clean-up. There are a lot of skills that 1-shot teams in the upper echelons of PVP. Nothing 1-shots a good Reina player.

Still, she's not commonly used in PVP for a myriad of reasons. You can make her work, and best of all you'll be unique in your team, but you will have to work at it. All of that being said, you already have a lot of powerful PVP units. I suggest just running one of them. :)

Naila is an absolutely monstrous unit that is powerful in ALL aspects of the game. You even have her UW, making her all the better. In pvp, she has the unique ability to dive into the enemy backline, making her redirect everyones ability often right off the side of the map. As a tank, this skill is far more valuable than most players realize when starting off.

Epis is the dive queen, dipping to the back then reaking absolute havoc with her defense shread and block ignore. She's also outstanding in PVE with her AoE. She really likes someone who can group enemies up in PVE(Gau, Maria), but PVP she's happy to just wreck people 1 at a time. she's a solid main dealer if Reina left a bad taste in your mouth.

Clause, Frey and Kasel are GOOD units. This is an oddity in King's Raid. The starter units are actually all good(though roi requires good gear to be good). Frey, Laias and Kaulah are the 3 best healers for the widest array. Though Cassandra may shake that up. That being said, with the units you have, i highly suggest running Naila, Clause, Reina, Frey. Sack Reina for Epis when you get your team to 5* and pick up Jane after she pops out of her inn to replace Clause. That's what I'd run in your shoes. After that you can pick up whatever units you like when you push into T1+.

G'luck out there!