It can be a bit overwhelming in picking what students in Blue Archives you should level for PvP also known as Tactical Competition. The reason why I am going over low-star students is that not everyone will have all higher-star students when starting out so there higher chance of having some of the lower-star students. This is also the reason I am not including students you get from events.

The reason you would want a higher rank in Tactical Competition is that you will gain higher daily rewards along with gaining first-time rewards. The daily rank rewards are tied into tiers so matter which one you are in what kind of reward you will gain. The first-time rewards are broken up into the first time you ever gain this rank and the first time you gain this rank this season. So there is always an incentive to gain a higher rank as seeing that rewards for both are Pyroxene which you use for rolling new characters. There are also daily coins you gain from daily rewards and winning defense battles.

There are a lot of students to choose from so I had this issue when I first started playing myself to pick the right ones. Just having the few right students could increase your chance to win a match in PvP or at least force it into a draw. Blue Archives PvP is divided into attack and defense. If you win in attack you swap ranks with that person. If you lose in defense you also swap ranks with that person. If the time runs out then whoever has the highest health wins of their striker students wins.

So I will be going over some good lower-star students to level if you want to focus a bit more on PvP elements of Blue Archives. As you would want to keep winning both attack and defense to keep getting daily rewards.

5. Akashi Junko

For damage dealers, Akashi Junko is a great choice. Her ex-skill (I'm Hangry!) deals damage in AOE which is good along with dealing a good amount of damage. Large AOE abilities are valuable for PVP in general as you would want to clear the field as fast as possible or at least remove all their damage dealers quickly. Her normal skill (Don't Talk to me When I'm Hungry!) is a great survivability skill as it gives her up to 24.3 seconds of being invincible when her health drops to 20% or lower. Just being invincible makes it so that she can soak up damage that could be for someone else and deal more damage before she has to leave the field. Her passive skill (Tiny Advantage) gives an increase in evade up to 26.6% which can be upgraded by Unique Equipment (Diner's Outlaw) which adds up to flat 304 more evade to her. Her unique item (Gourmet Notebook) increases her damage by 800 and upgrades her normal skill to decrease her ex-skill cost by 4 for 2 uses but this may not be in the game yet. Last of all her sub-skill (Hungry Foodie) give her miss health damage bonus. This ability is similar to Tryndamere from League of Legends ability Bloodlust which gives him bonus damage based on missing health. The sub-skill also works great with her normal skill as she can have the max bonus from the sub-skill for a while. Overall this character provides good damage abilities and survivability.

4. Izayoi Nonomi

Another good damage dealer is Izayoi Nonomi. The biggest bonus of having her on the field is that her ex-skill (Punishment Time!) hit everyone on the field most of the time as it is a large fan AOE. Having such a large AOE could clean out most of the enemy's damage dealers making it easier to win the match. Her normal skill (Ta-da! ☆) increases her damage every 30 seconds which lasts for 20 seconds. Her passive skill (Tsk Tsk, Shame On You!) increases her critical damage up to 26.6% this ability can be upgraded by unique equipment (Little Machine Gun V) which increases critical damage up to a flat amount of 3800. Her sub-skill (Squeaky-Clean Sweep) is only useful I think when fighting someone that has a tactical support rider out as it gives only bonus to large enemies. Overall she is a solid pick for a damage dealer for PvP.

3. Hayase Yuuka

Why Hayase Yuuka picked her is because of her useful role as an off-tank for your team. Her ex skill (Q.E.D.) is on the cheaper end of the cost of 3 which gives her a barrier that makes her tanky along with her passive skill (Optimal Solutions) which at max level gives her an increase of DEF by 26.6%. The passive skill (Optimal Solutions) can be upgraded by Unique Equipment (Logic & Reason) which gives an increasing block up to 1900. She also has a unique item (Yuuka's Scientific Calculator) that also gives her DEF+500 at T1 and then increases her normal skill at T2. The normal skill (I.F.F) deals damage to a single enemy every 15 seconds but with the upgrade it will add evade by up to 33.8% for 10 seconds. Her sub-skill (Calculative Mind) is very not useful as playing PVE she rarely takes cover for me. So overall she is a good pick for PvP for a tanky character as she is a good low-star character with good defensive stats.

2. Sumi Serina

Sumi Serina is the only support student I have on this list. The combination of her ex-skill (Intensive Care Set A) which gives one ally healing and her normal skill (Urgent Rescue Set B) which heals one ally every 35 seconds makes her a great support that will keep anyone alive for a very long time. Her passive skill (Ministering Angel) even increases her healing up to 26.6% and this skill gets upgraded by a base amount from Unique Equipment (Tactical Therapy) up to 1848 healing. Her sub-skill (Guardian Angel's Smile) has few use cases as it does give CC resistance. She is a vital student to have if you do not have a higher-star student to replace her.

1. Kasuga Tsubaki

My top pick is Kasuga Tsubaki to have for PvP. She is probably one of the tankiest characters you can have. Her ex-skill (Deploy Tactical Shield) increases her defense up to 44.9% but at the same time taunts all the enemies for up to 6.2 seconds. The taunt is a viable CC is it can knock others out of their ex-skills along with making everyone focus on her. Her passive skill (Fortitude) increases her defense up to 26.6% and her sub-skill (Expert Reload) decreases incoming damage when reloading up to 45.6%. Her Unique Equipment (Sleep Companion II) upgrades her passive that adds flat attack speed which increases her damage output. Her normal skill (Sleep Cures All) is one of the strongest self heals in the game which almost full herself as she can recover up to 663% of heal when below 30% heath one time. She also has a defense of mythic so there are not a lot of good choices to eat through the defense if you do not have a lot of students with mythic damage. Because of how tanky she is, she is still used in the highest ranks of PvP. Having Tsubaki and Serina can make matches end up in a tie because each side could not clear each other fields.

Conclusion

Overall these students are the ones I would recommend to a new player that does not have a lot of character. As Kasuga Tsubaki, you probably will not need to switch her out for a different tank. Hayase Yuuka will be good for other parts of the game as an off-tank. Sumi Serina is a great healer so no matter what you will find a use for her. Akashi Junko and Izayoi Nonomi are good damage dealers though I would recommend prioritizing leveling only one of them if you do not have the other damage type covered.

My highest rank was 12 but I mostly hover around 40 to 240 as ranks can fluctuate. So I hope my insight into the game will help boost your rank in Blue Archive.