Fans have wondered whether Zenitsu ever got to realize his dream of becoming a Hashira at all. Unfortunately, the answer to this question would be, no, he did not. Zenitsu, along with Tanjiro and Inosuke got way stronger than average corps members with training.
Why Zenitsu Falls Asleep in Demon Slayer? Just need this type of strength while sleeping. Zenitsu, while awake, is aware of his surroundings, and can sense demons quite efficiently with his 'Enhanced Sense of Hearing', but when it comes to even slight contact with a demon, he blacks out.
When asleep, however, Zenitsu is able to let go of his paralyzing fear and anxiety and let his prowess shine through. In this way, Zenitsu is similar to Rock Lee from the manga and anime series Naruto, since they both need to transport themselves into a different headspace to tap into some of their greater powers.
So in a nutshell, Zenitsu wasn't able to master the other five forms, but later in the Infinity Castle Arc, during the battle with Kaigaku, Upper-Rank Six Demon, he created a Seventh Form: Flaming Thunder God.
Tanjiro did not become a Hashira towards the end of the series but defeating Muzan is enough reason to say that he is Hashira level. He was trained by Urokodaki and learned the Breath of the Water, which is considered a difficult sword technique. He mastered Full Focus Breathing, which only the Hashira can do.
Exploring Zenitsu's fighting abilities in Demon Slayer
Zenitsu has perfected the first form only and is seen performing it only when he's unconscious. But the manga shows that he can fight without fainting or going unconscious. Later in the manga, Zenitsu fights an Upper Moon 6 demon named Kaigaku.
Kaigaku realizes that Zenitsu is much more versatile and skilled with his swordsmanship than before. However, he still believes that no matter how much Zenitsu trains, he can never defeat an Upper Rank like him. Zenitsu then is slashed by Kaigaku with the Thunder Breathing, Second Form: Rice Spirit.
At one point or another in the manga, all nine Hashira in Demon Slayer encountered an Upper-Rank. Of the three Hashira who were killed by Upper-Ranks -- Rengoku, Shinobu and Tokito -- Shinobu was the only one who was killed almost instantly when she encountered Doma, Upper-Rank Two.
Tanjiro Kamado does not become a hashira / pillar of the Demon Slayer corps. In the final chapter of the manga, he defeats the Demon King, Kibutsuji Muzan thereby eliminating all the demons, and in extension eliminates the need for Demon Slayer corps and Hashiras altogether.
Tanjiro decapitates Akaza with the Hinokami Kagura: Setting Sun Transformation. Akaza was bewildered, wondering how Tanjiro did not have any fighting spirit, comparing this feeling to fighting against a plant. He acknowledges that Tanjiro surpassed his speed.
Gyomei Himejima is the strongest Hashira in Demon Slayer. This fact has been established in the manga as Tanjiro, Inosuke and Zenitsu all agree that he is the strongest member of the Demon Slayer Corps. His strength was showcased during the fight against Kokushibo.
Tanjiro's rank in the Demon Slayer Corps is Kanoe, the fourth up from the bottom. He doesn't receive a higher rank for the remainder of the series. His rank is specified during a conversation with Inosuke held during the Entertainment District arc.
Seventh Form: Flaming Thunder God) - The personal creation of Zenitsu Agatsuma. The user dashes forward at blinding speeds and unleashes a singular forward slash at a low stance, which is seemingly accompanied by a yellow Japanese dragon shaped like a lightning bolt.
Zenitsu has honed this ability to the extent of being able to repeat the dash multiple times in quick succession. He usually goes for Six Fold, which means six dashes but has been able to use Eight Fold to dash eight times within one use of the technique.