As there hasn't really been any proper reviews talking about every OVA as i have heard they are stopping at 11, i decided to write a review summing up every OVA, and I'm going to assume that you are reading this after watching all 50 episodes of the series, and seeing if this is worth checking out.
-Story--8-
The story in these OVAs carry the same quality as the main series, but with it obviously progressing. The first few episodes are to give you a re-cap on each character and their personality, which i believe is fine as this OVA started 6 years after the main series ended, but as someone who may have come straight from the main series this may be a bit bothersome, but nothing i could say is a bad thing as it was intended to re-cap people after six years. These first episodes also introduce us to a new group of enemy, and the people behind it, who, like Ragnarok, are after the strongest disciple, Kenichi. This new group, named 'Yami', are what you may see as Ragnarok but with a stronger cast of enemies, which is true, but as a result the battles are more intense and complex. The episodes following the first few are mainly battles against this new group, and as a result we see not only Kenichi, but his friends develop their skills and become stronger. In some cases, after fights we see what some people may call 'fillers', but are just really us seeing the result of the fight prior to that episode, and maybe some other relevant things, so i wouldn't call them fillers. The ending as also quite satisfactory, but that also depends on the person, so watch to see for yourself.
-Art--8-
I thought that even though fights got more complex and maybe harder to track, the art was fluid and focused on the main points of the fights. Speaking of fights, the debris and impact of punches were detailed, and were not skimped on, allowing the fight to look better and enhance your enjoyment. As for the art in itself, they didn't make much changes from the original art, which i thought was great as not only did it differentiate itself from the type of art-style being used around this time, it at the same time felt familiar and didn't detach itself from the main series, but i can say i felt the art was brightened up a little, which i thought was a change for the better.
-Sound--7-
I thought the sound was average, but didn't hold back the anime. The OPs and endings suited the anime and the sound amplified the atmosphere that any particular scene was going for, and in battle scenes made the situation more tense and made the situation feel more desperate if needed, and made the viewer feel more calm when Kenichi is in school for example. The sound also sounded different, obviously with the exception of the OP and ending, they went for different songs which made it not feel repetitive and maybe just a quick thing made using recycled material.
-Character--8-
Obviously, the characters are the same in the OVA as in the main series, but i'll just go over them and maybe point out anything that made the anime better or worse.
First we have the main character, Kenichi. Kenichi is usually shown as a good natured, kind boy who prefers not to use violence for no particular reason, but uses his knowledge of Martial Arts if necessary. Despite being called 'History's Strongest Disciple', in times out of fighting he is usually shown as timid and apprehensive at times, and having hobbies of reading books and gardening, he is usually mistaken as a regular person and often laughed at. In the OVA, due to the new group 'Yami' targeting him, he is said to have trained 'three times more' than usual, with the outcome of him getting stronger. I thought although not much has changed about him, it meant that he had kept his personality which i thought was great, as he had a personality which was unique to the series and OVA. All-in-all, nothing bad about this character.
Next, we have the other main character, Miu. Miu is also shown as kind-hearted and caring for her friends and family. Her parents died when she was very young and has been under her Grandpa's care and training since around the age of six. She is shown to be highly skilled at Martial Arts and be very money efficient, and also do most chores in the dojo, until Kenichi helps. Miu is very clearly what you may call the 'Fan Service' on the anime, and in the OVAs has been more prominent with her and other female characters, which is fine as it doesn't get in the way of anything, and for most men is a plus, but i know some people who watch anime don't appreciate fan service, so if you despise it, Miu may hinder your enjoyment. Apart from that, like Kenichi, not much has changed about her, she doesn't get any stronger as well, but one thing i would like to say is that she is shown a bit more as a main characters, always being with or fighting with Kenichi when he gets into one.
As for the other characters, not much has changed either. All of the masters have still got their unique personalities due to having different Martial Arts stemming from different places, which is good as there's no sense of repetition between the characters, and are all also predictable but in a good way that you can get some humor out from it. The new characters introduced are a bit similar to the ones from Ragnarok, but again due to having different backgrounds in Martial Arts do not feel samey, but i thought the OVAs didn't really tell us enough about the characters to really feel for or hate, and felt at times may have felt a bit rushed.
-Enjoyment--9-
As someone who enjoyed the main series, i enjoyed this one just as much as that. Being a sort of continuation of the series, it didn't feel detached and isolated, and felt like it was part of the main series, which was great as it brought a sort of sequel to the series. One thing i would like to point out is that it did feel like the OVAs were brightened up compared to the main series, which made it feel less heavy, which is a change for the better i felt. Being someone who watches Shounen regularly, there's nothing much i can complain about as it has no major faults and does things well at least. If there was one thing i personally didn't like, it would be the fact the antagonists felt a bit rushed.
-Overall--8-
This OVA manages to hold up people's faith for a 'second season' and re-ignites the flame in peoples hearts for the main series. It manages to keep up the story well and lets us sink into the arc that this OVA is based on, as well as introduce us to a new one, which is a piece of evidence pointing to more content. Although there are few faults, the OVA manages to carry on the soul of 'History's Greatest Disciple Kenichi'. All-in-all, a great OVA with a few noticeable faults.