Since I don't know the exact nature of 'zettai ni yatte wa ikenai isekai novel', it's hard to give precise recommendations. However, there are many isekai novels out there. 'Overlord' is an isekai where the main character has to deal with ruling an otherworldly kingdom and has to abide by certain in - world rules. Another one could be 'That Time I Got Reincarnated as a Slime' which has unique world - building and rules for the characters to follow. These might have some similarities in terms of world - building and rule - following as the unknown novel.
Given that I don't have a full understanding of 'zettai ni yatte wa ikenai isekai novel', I can only make general suggestions. Some isekai novels like 'Log Horizon' could be considered. It has a complex world with its own mechanics and rules that the characters need to respect. Also, 'Grimgar of Fantasy and Ash' which has a group of characters trying to survive in a new world with various unwritten and written rules. These novels might be somewhat similar in the sense that they have their own unique worlds with rules that are important for the story.
I'm not sure specifically as I haven't read this particular 'zettai ni yatte wa ikenai isekai novel'. It could be about various things common in isekai novels like a protagonist being transported to another world but with some kind of moral or rule that they must not do certain actions (as the 'zettai ni yatte wa ikenai' part might imply).
Well, without having read the actual 'zettai ni yatte wa ikenai isekai shoukan novel', it's difficult to give a detailed account. However, given the title, it could be about a character who is summoned to an isekai world and discovers there are certain actions that are strictly prohibited. Maybe it involves a protagonist who has to navigate this new world while avoiding these forbidden deeds to achieve a certain goal, like saving the isekai or getting back home.
As I'm not familiar with this specific 'zettai ni yatte wa ikenai isekai shoukan novel', there's no way for me to determine the main characters. It could be a typical isekai setup where there's a young male or female protagonist who gets summoned to the other world and has to face various challenges, but without reading it, this is just speculation.
There are several works that share similarities. For instance, 'Re:Zero − Starting Life in Another World' has the concept of a character being in an isekai world and facing numerous challenges. The main character has to constantly adapt and find solutions, much like in 'isekai wa smartphone tomo ni web novel'. 'Grimgar of Fantasy and Ash' is also similar as it focuses on a group of characters in a new world trying to survive. And 'How a Realist Hero Rebuilt the Kingdom' where the protagonist uses his modern - day knowledge, somewhat like how the smartphone in the other work might provide useful knowledge, to make changes in the new isekai world.
As we don't know the full details of the 'isekai wa smartphone to tomo ni' novel, it's challenging to give exact similar novels. But if it has a modern - world - meets - fantasy - world aspect, perhaps 'Ready Player One' could be considered in a way. The main character enters a virtual world which is different from his own, just like the isekai concept of going to another world. However, this is just a loose comparison as we lack specific details about the original title.
There are several web novels that share some elements. 'Re:Zero − Starting Life in Another World' is somewhat similar in the sense that the main character is in an isekai setting. Although the character isn't a 'yankee' type, the theme of facing challenges and forming relationships in a new world is there. Also, 'Sword Art Online' has an element of being in a different world (virtual in this case) and dealing with different entities, which could be related to the overall theme of the given web novel.
One similar work could be 'KonoSuba'. It also has elements of being in a different world and the main characters have to deal with various challenges using their own unique skills. Another is 'That Time I Got Reincarnated as a Slime'. The protagonist is reborn in a new world and has to adapt and make his way, much like in 'isekai wa smartphone to tomo ni web novel'.
One similar light novel could be 'KonoSuba'. It also has elements of isekai with a comical take on the genre. Another might be 'Re:Zero − Starting Life in Another World' which has an interesting take on the isekai concept though not exactly the same as 'isekai wa smartphone totomoni'.
Since we don't really know the details of 'shounen yuusha wa isekai wo gyuujiru novel', it's a bit of a stretch to recommend similar ones precisely. However, in the isekai genre, 'Re:Zero − Starting Life in Another World' is well - known. It has a young male protagonist who has to face many difficulties in an isekai world. Also, 'Konosuba: God's Blessing on This Wonderful World!' has comical elements along with the isekai setting which could potentially be somewhat similar depending on what 'shounen yuusha wa isekai wo gyuujiru novel' is really about.
Yes. One similar light novel is 'That Time I Got Reincarnated as a Slime'. It shares the isekai concept and has an interesting protagonist who adapts to a new world. Also, 'Overlord' is a good recommendation. It has a powerful protagonist in an isekai world, like in 'isekai wa smartphone', but with a different kind of power dynamic and story development.