What can I do once I get some character to level 40 to enhance them?

I am the definition of a casual player when it comes to Fire Emblem Heroes. I have been logging in since it came out, so I have many 5 star heroes at level 40. I mainly just like to collect the characters.

That being said, once I get them all to level 40, other than merging them with other level 40 heroes of the same person, how can I improve them? I have used the SP on them all to buy the skill upgrades... but that's it. Should I be trying to fill their skills by making manuals out of people so they don't have any blanks? What do I do with Heroic Grails? Is there something I can do with items? I don't think I've ever used any items or accessories or anything.

I know I'm a strange case, but I feel like I have a bunch of stuff and I don't know what to do with it after having my people all hit level 40. I tried to find a "how to play" guide that explained but couldn't find anything.

Solution 1:

once I get them all to level 40, other than merging them with other level 40 heroes of the same person, how can I improve them?

There are multiple ways to improve heroes.

1. Merging: As you already mentioned, you can merge heroes. Your heroes only get stronger if you are merging them with another of the same hero of equal or better rarity. In other words, to improve the stats of a 5 star hero, you must merge it with the same 5 star hero. Merging with a lower rarity hero is possible too, but only awards you with SP. SP can also be earned by killing enemies instead.
   
   Merges don't carry over to the next rarity level. In other words, if you have a 4 star +10 merged hero, unlocking their potential to 5 star will reset their level to 1, without the +10 it got from merging. To have a 5 star Level 40 +10 hero, you need 11 of the same 5 star hero. You can't merge 3 or 4 star heroes, then use Unlock Potential instead.
   
   

2. Min-maxing Assets and Flaws: This is somewhat related to merging. When you receive heroes, they may have 1 asset and 1 flaw, or neither. A hero with a Atk Asset will have higher Atk than the same hero without, and even more than the same hero with a Atk Flaw. Some heroes benefit more from certain Assets than others, while suffering less from certain flaws than others.
   
   For instance, with 23 Spd, Reinhardt is one of the slowest heroes in the game. His unique weapon, Dire Thunder, allows him to strike twice in a row in exchange for a -5 Spd penalty. At 18 Spd, he has the third-lowest speed of all units (lowest is 16 Spd without Flaw or Asset). As a result, having a Spd Flaw (15 Spd) doesn't hurt him much, and having a Spd Asset (21 Spd) would be nearly useless to him. On the other hand, due to his offensive nature, a Atk Asset or Flaw would affect his performance the most.
   
   When you manage to pull a hero with a better Asset, you can merge your old hero into the new one. The results are the following:

   • The new hero inherits all previous merges, and gains another +1 unless they inherited a +10. It makes no difference which hero you merged into which, as all merges are preserved (assuming both heroes are of equal rarity).
   • The new hero inherits everything from the old hero, except SP, level, and stats. This includes skills inherited from other heroes, skills learned by spending SP, and Refined weapons. Remember to equip the old hero's skills on the new one.
   • Your hero will lose their Flaw. At +1, heroes receive enough of a stat boost to completely eliminate their Flaw. Thus it no longer matters which Flaw they used to have.
     
     

3. Skill inheritance: Not all heroes come with good skills, and some come with skills that don't fit them well. Most heroes also lack skills for some slots. Some heroes only come with Lvl 3 of skills that now have 4 levels (like Alphonse's Death Blow 3), and some weapons — while weaker than a hero's unique weapon — may be more useful (like the Brave Weapons+, which allow slow units to strike twice in a row, or fast units to strike up to 4 times). Keep in mind that not all skills can be inherited, and some skills can only be inherited by certain types of heroes.
   
   To inherit a skill, you need a hero that can learn the skill. The hero doesn't need to have spent SP to learn the skill. You also don't need to turn the hero into a Combat Manual before their skills can be inherited. You can only inherit the skill if your hero can learn it at their current rarity level. For instance, you can inherit Renewal 3 from Jakob or Lissa only if they're 5 star, while Fae and L'Arachel can teach you that skill at 4 star instead.
   
   You can inherit up to 4 skills (used to be only 3, back before level 4 skills existed), and must inherit all prerequisite skills too (for example, to inherit Death Blow 4 your hero must either have Death Blow 3, or you must inherit Death Blow 3).
   
   Once you have inherited a skill, you'll need to spend SP to learn them. If you run out of SP, you can gain more by killing enemies.
   
   

4. Seals: Seals are essentially S-slot skills. Many skills exist as Seals, and some skills are Seal-exclusive. Many Seals are cumulative, i.e. equipping both Death Blow 3 (A-skill) and Death Blow 3 (Seal) will give you a boost of +12 Atk (instead of only +6 Atk) when your hero initiates combat.
   
   You can only own 1 of each Seal, and only 1 hero can equip a given Seal. In other words, you can only have 1 hero with the Death Blow 3 Seal.
   
   

5. Weapon Refinery: You can use Refining Stones and Arena Medals to improve the weapons your heroes already have. Some weapons require Divine Dew instead of Refining Stones. A refined weapon is guaranteed to give you +3 HP along with some other benefits.
   
   This is particularly useful for healers who don't know Wrathful Staff (their damage is halved compared to other units). Healers who know Wrathful Staff can refine their weapon to gain a Dazzling Staff effect instead (allows you to attack without the enemy counter-attacking).
   
   

6. Ally Support: You can have 2 heroes support each other. When next to each other, they gain +2 of certain stats (depending on Support level). When they're 1 space apart, they only gain +1 instead. A hero can only have 1 support partner. The stats gained are:

   • C: Res
   • B: Res/Def
   • A: Res/Def/Spd
   • S: Res/Def/Spd/Atk
     
     

7. Summoner Support: Similar to Ally Support, but is always active (since the Summoner is not a playable character) except during Defensive battles in the Arena or Aether Raids. Only 1 Hero can have Summoner Support (3 if you have a Feh Pass subscription), and heroes can have both Summoner and Ally Support at the same time. The stats gained are:

   • C: HP +3, Res +2
   • B: HP +4, Res/Def +2
   • A: HP +4, Res/Def/Spd +2
   • S: HP +5, Res/Def/Spd/Atk +2
     
     

8. Blessings: You can confer a Blessing to your heroes. If the current season matches the type of Blessing, and the hero is in the same team as a Legendary or Mythic hero of the same Blessing type, that hero will receive a stat bonus. The bonus depends on the Legendary or Mythic hero in the team.
   
   

9. Dragonflowers: You can use Dragonflowers to improve all stats once (old heroes can improve all stats twice). You can't choose which stats to improve, as it's fixed. It's just how it sounds: when improved 10 times, Alphonse at level 40 will have the following stats:

   • HP: 45 (43 +2)
   • Atk: 53 (35 +2) (+16 with Fólkvangr)
   • Spd: 27 (25 +2)
   • Def: 34 (32 +2)
   • Res: 24 (22 +2)

What do I do with Heroic Grails?

Heroic Grails are used to summon heroes that can't be summoned with Orbs. Most are heroes that were given as reward for winning a Grand Hero Battle, or for reaching a certain score during Tempest Trials.

Since these heroes can not be summoned with Orbs, Heroic Grails are the only way to merge these heroes to +10.