Shirihama Kenichi is a weak scaredy-cat, and his status as the karate club's punching bag has earned him the name of ‘Weak Legs'. One day Kenichi meets Miu and, impressed by her skill after she effortlessly throws him to the ground, he follows her to the Ryouzanpaku dojo. There he finds five great masters of martial arts, and driven by his desire to become stronger, he begs them to accept him as their student - though it won't be easy. Kenichi endures harsh training (and injury) from Akisame - the philosophizing Jujitsu master; Apachai - the Muay Thai ‘God of Death'; Kensei - the ecchi Chinese Kempo Master; and Shigure - the weapons prodigy. Finally after proving his determination, he is accepted by Shio - the 100-dan Karate Master, who had initially wanted nothing to do with him. Now Kenichi walks the long and arduous path to becoming a master himself, all whilst trying to protect those he cares about from anyone who would dare to harm them.
These two manga are very similar, and not just because they are about martial arts. They have a very similar feel to them. Both Otawa and Kenichi in the pursuit of getting stronger, end up in dojo's that are more than they expected, and they both have super strong grandfathers running them. They both have a love interest in the granddaughter, whose also a strong fighter, and both of them have to go through intense, and strange training, in order to get stronger. Although Strongest Disciple is a bit more comedic, and seems to cover a wider variety of martial arts, if you liked one, you should try the other.