With that said, I thought it would be fun to make a combat prowess/powerlevel tier list for this series, so let's get started. Here's my tier list for the series along with my rationale for each one.
1. Ikusa Ayasaki
While Ikusa does not have much in terms of feats as we've never actually seen him go toe to toe with any of the heavy hitters in the series, it feels like he was basically designed to be the Seijuro Hiko of the series (if you're familiar with Kenshin). We have actually only seen him square off (unscathed) against Midas, destroying robot Eight with a kick, dodging and destroying Athena's magical hammers and then fighting against a possessed Yukiji with some assistance from Hayate -- however, despite his lack of feats, the amount of hype surrounding his character and the fact that he has never even been in any real type of trouble in a combat situation puts him at the top of this list by implication.
2. Yozora Housen
If we were to disregard Ikusa's existence, then there is no doubt in my mind that Yozora Housen rightfully deserves to be at the top of this list. However, I like to keep the author's own headcanon (as I perceive it) in mind -- which is why I rank Ikusa above her.
Unlike Ikusa, Housen has various feats throughout the manga to her name. She once took on Hayate, Isumi, and Tama all at once and managed to escape unharmed. She was also fighting pretty evenly against a full powered Isumi and a weakened Athena although she was having trouble based on Hisui's assessment.
Also, Housen is shown to be able to utilize the hands of Midas and some limited degree of magic unlike Ikusa who basically just brute forces his way out of any situation. Let's not forget that she also managed to defeat Machina off-screen with some difficulty.
3. Hisui Hatsushiba
Pre-power up, i would actually rank Hisui pretty low as a fighter. However, given her ruthlessness and the power-up that Housen granted her, she sits comfortably at number three in my list. Also, I don't think there is a huge gap between her and Housen. The reason I rank her below her servant is because Hisui is a more aggressive and thus, less tactical fighter. We see proof of this in her sword fight with Hayate wherein Hayate had figured something out about her movements and was just about to defeat her before Yozora interrupted the fight.
I like to think of the power difference between Housen and Hisui as similar to Supergirl vs Superman. Supergirl may be more ruthless and generally hits her enemies harder than Superman, but that doesn't mean she's actually more powerful than her cousin.
4. Isumi Saginomiya
Let me get this straight -- Isumi is strong -- very strong, but she's more like a glass cannon. Her feats are pretty evident all throughout the manga. She can effortlessly blow up reinforced gates and other things with her magic and she can snipe a king's jewel from god knows how far away.
By her own admission, her power level is about on par with Athena, but I think Isumi tends to sell herself short because of her personality. Let's not forget that she managed to take on a powered up Hisui for a little while and that her appearance is often the reason that the bad guys decide to regroup and retreat.
Of course, I do not think she is any more durable than an average girl her age, as we've never actually seen her engage in close combat with anyone worthy of note in the series. As such, she is probably not very damage-resistant but makes up for this with defensive magic and just being agile enough not to get hit in general.
5. Himegami Aoi
... Just why did his name change from Akane to Aoi anyway? Sigh... Hata... anywayz, I rank Himegami below Isumi for one simple reason: he does not appear to be able to use magic proficiently. As a close combat fighter, he's shown to be stronger than Hayate as he handily defeated him while Hayate was already in berserk mode for Nagi's sake -- of course, perhaps we should also consider the fact that Hayate's feelings for Nagi were quite confused at that time, which means he wasn't at his best.
He can even hold off strong magic users like Isumi and Athena combined at once. Of course, I still rank him below Isumi because he never actually defeated her and he was already having trouble fighting against Isumi and Athena until Hisui bailed him out.
Himegami can also fly and is possibly able to use some limited form of magic as well as having his own special attack.
6. Athena Tennousu
I'm ranking Athena below Himegami because while being touted to be a very strong magic user as well as a formidable swordswoman, she performed quite poorly in the actual combat situations she has been in -- especially at the finale (yes, she wasn't at full power, I know).
Pure speculation, but Athena should probably be at the same power level or perhaps even stronger than Isumi as a magic user, but the problem is that she hasn't been constantly in combat situations that required the use of her power unlike Isumi. Furthermore, when called on to actually fight, she seems to prefer to rely on Isumi to do the fighting for her -- or at least help her out.
All we know is that this guy defeated a non-berserk Hayate pretty easily, which means he should be stronger than Hayate normally and that he actually managed to give Housen some trouble and broke her visor during their fight. With that said, we haven't seen much about how he fights so I'll just blindly assume that any of the strong magic users in the series can take him out.
8. Yukiji Katsura
As the elder of the Katsura sisters, Yukiji is rather powerful on her own. Although she regularly wrangles with her sister with no clear winner between them, her greatest feat would be when she was possessed by a demon and she managed to surprise even Ikusa with her raw strength. Also, Hayate has no qualms about going all out and actually trying to hurt her because he was very sure in his mind that she could take it. While possessing no magical items nor magic of nay kind, Yukiji is perhaps something like the female version of Ikusa who can simply take on anything with pure brute strenght.
9. Hinagiku Katsura
Hinagiku is probably not far behind her sister, but I'm placing her one rank below the elder Katsura on the tier list simply because I feel that Yukiji is the more experienced fighter and acts calmer when in a fight (I believe this is important when assessing power levels in a shounen series). With wooden masamune (broken by Himegami) and Shirosakura at her disposal along with her natural combat ability and instincts, Hinagiku Katsura is definitely no slouch. While one could count it as a surprise attack, she even managed to take down the more powerful Himegami using a simple bokken and the Shirosakura as a hoverboard.
10. Hayate Ayasaki
Sure Hayate is far below on this tier list, but I think our titular combat butler deserves some mad respect for various reasons. Normally, Hayate is strong enough to handily take on mooks and Robot Eight (until one day when he couldn't), but we always see him in all sorts of trouble and needing someone else to bail him out (usually Isumi, Hinagiku, Athena, or even Nagi) when he is in a serious fight.
The one thing that triggers his natural fighting instincts would be seeing or knowing that his lady (which can only be Nagi) is in danger. This is when we see the best of Ayasaki when he enters his berserk mode. Arguably, he would have been able to defeat Machina or at least give him some trouble if their fight had gone on.
With that said, I think that Hina is still a bit stronger than him because of her ability to command her weapons at will and being a bit more resourceful than Hayate in a fight. Hayate beat her once not by taking her own directly but by using her fear of heights to end the fight without ever fighting.
Hina appears to view Hayate as an equal when it comes to combat and it's implied that Hayate probably feels the same about her.
Hayate also has a super strong nuke-like attack called "Hayate no Gotoku" that propels him to Nagi's side like a gust of wind. The problem is that he has no control over this attack and he needs Nagi to call on him in order to activate it.
Well, that concludes my tier list. I might have missed a few people like Nonohara, but I think they're a bit too insignificant in the series over-all to take into account anyway.
What do you think? Agree? Disagree? Do you have your own tier list? Share your thoughts in the comments and see you next week!
For this week's fanart corner, we have some fanart of mai waifu from Denzil. Thank you for the Christmas Card! I love the Santa Nagi that came with it. It came in a bit late due to postage and customs in my country, but I really love the fanart! Thank you again!