Like most other games, the player character (the "Ghost Agent") is subject to a levelling system.
Key stats for the character are Health, Attack Spirit, and Defense Spirit. The maximum for these stats are determined by Ability points. [link to ability points article]
Health and Attack Spirit are replenished naturally at a rate of +1 per minute, while Defense Spirit replenishes at a rate of +2 per minute. It is also possible to instantly replenish these stats using appropriate items.
Health: allows progression through the storyline. For every Investigation, a set amount of health is deducted from the player. When the player no longer has sufficient health, progression through the story stages is halted.
Attack Spirit: allows the use of Daemons for the purposes of battling other users, be it for Silver Pieces or Stones. The available Attack Spirit determines the Daemons from the Attack queue which can be called upon for the battle. Each Daemon requires a set amount of Attack Spirit to be deployed. The Attack Spirit is depleted by battle.
Defense Spirit: determines the Daemons which make up the Defense squad, which counters challenges by other players. This stat is depleted when other players fight you in battles.
Ways to gain ability points:
1. Each level gives you +3 ability points
2. In every other level, you get an extra crewmate slot. This gives you +5 ability points
3. You get +5 ability points when you join a guild.
4. You can get a lot of ability points by completing the story, not 100% by the way.
Ways to reallocate stats:
1. Adding/removing crewmates
2. Joining/quitting guilds
3. Beef bowls
To know how much ability points you have... You could:
1. Investigate in the story until you have no hp left and still click investigate. It will show you a screen wherein you could see your total health, attack and defense spirits.
2. The total hp can be seen in the main screen and when you investigate in the story. The total attack spirit can also be seen by pressing menu-daemons-attack team. For defense spirit, defense team.
3. When you add a crewmate, you can add ability points; and there, you can also see your total ability points for each category.
1. Stop in the 60s or 70s to complete sealstones
After you enter the level 81+ battlefield, unless you have a very intimidating or bell-tier leader, you cannot keep “hot” seal stones most of the time esp. those of the latest sealstone deamons, except probably during events when everyone else is busy using their attack spirit for something else.
Therefore, people usually recommend that you stop levelling up during this stage in order to unseal or maximize the skills of Lady Suzuka, Kiri, Ramiel, Hijod etc. This saves you the trouble from having to complete this task much later against high-level players.
2. Rush to 81 and beyond
The advantage of not stopping in the 60s or 70s is that you can gain much more ability points. This allows you to play in events more efficiently. Your use of sw, remedies and divine nectars is more worth it because of a larger ability point pool.