May you help me solve my swordmanship dilemma?

I would wait for a Soleil, at least for a long-term investment. Hana is good and all, but Soleil is a powercreep unit with higher BST and a better spread: a +spd IV brings her up to 38-38 on offence.

With so much investment, I'm kind of questioning whether it would be worth it. There are better sword options out there...

Wouldn't Firesweep Sword better? Since she can literally die even on player phase due to her defense? Now you have Heavy Blade so you don't need that slaying axe's effect, and can go Hit and Run to give her more safety. Also I say her boon doesn't matter, have her support that give hone atk or spd depending on which boon Hana is.

If you really want to use Hana ( which is a great choice by the way ) i think you should take a speed boon with spd refinery. With that she will get 52 atk and 47 spd. I think the atk is enough to activate heavy blade, if not you can always buff her even more.

By having so much spd, you dont have to worry about if you can double the enemy or not, you could double almost every enemy in the game. Desperation is of course preferred after she gets weakend. With Galeforce, she would be an Infantry Brave Roy, but with much more spd.

I know, high atk is tempting, but who has more than 51 atk? Maybe if someone buffs themselves, but you can always do the same. At the end its up to you, both stats are interesting.

If you were to take the atk boon, i should giver her at least an spd refinery to sill have enough speed to deal with most of the units.

For reference, her arena weight is unaffected by the Resistance bane. Occasionally, it can change how many merges they will need to get into a different BST bracket, but at minimal and maximum merges, it does not change (but it can for some units)

Onto the question of Hana vs. Soleil:
You should wait for Soleil because she is an attack boon Hana with only 1 less speed, which could be fixed with a speed boon or refined weapon. You could even put Life and Death on her to make her completely outshine Hana. However, Hana is much easier to acquire and get to a +10 merge, which is the biggest benefit she has.

Deciding on weapon choice:
Should you want to use Galeforce, a Slaying edge will do a great job of activating it, assuming you can attack your opponent twice AND have higher attack. It can also be refined for additional speed, attack, or defense, but you'll be forced to use desperation as your B passive.

However, Firesweep scales better with attack and can keep Soleil or Hana from getting hit when initiating combat, allowing you to use something other than desperation for your B passive, like Sword Breaker and Wrath for more damage, or Renewal and Drag Back/Hit and Run for better survival (Swordbreaker is the best option). Sadly, it can not be refined, so you'll be stuck with whatever attack, speed, and defense you had before, so you'll be relying more on your IV's in this case.

If you decide to use Hana:
- You'll want +Attack and -Resistance
- Easier to Merge and get ideal IVs
- Paper thin, dies to one attack from anyone, and special activations will kill her (on the bright side, she'll be almost unaffected by moonbow

If you decide to use Soleil:
- You'll want +Attack and -Resistance
- Harder to merge, but is a higher BST bracket by default
- Can take ONE hit from anything Red and Green (excluding buffed Blade-tome mages)

Conclusion:
In the end, you'll need to have both Hana and Soleil at five stars to make their best builds which include Life and Death and Firesweep sword. Soleil is by far the better choice because every stat she has will outshine Hana's, even with their best builds. You will eventually want to have a Firesweep sword on Hana, but on the off chance that you get a Soleil with +attack or +speed (and without negatively affecting each other), she'll be the better unit unless your Hana is already heavily invested into and merged to at least 5* +5