So Shiho already played Tomodachi Game with Tenji's friends before Tenji's father's death....

Sorry, I haven't read the beginning chapters for a while but where did it say Shiho played the game before? Tenji never said anything in ch 12 about Shiho was there when Tenji and his friend's played the game, only that the friends may have been doing it to win the bet to confess to Shiho. Also, she didn't seem to be aware that the game existed because when the kidnapper said "should we play a game" to Shiho, she didn't react to it. If she had already played the game she should have realized, or if not at that point she should have noticed when the kidnapper started talking about friendship vs family that she might have been in the situation because someone was playing the tomodachi game. The only thing she concluded from the talk with the kidnapper was that her father and the man probably have some kind of deal and since she's his family, the friendship part was probably about Tenji's father.

Tenji and Shiho's father's friendship was broken because Shiho's father chose his family bond (to save Shiho) over his friendship (to save Tenji's father, who was probably kidnapped before because he was snooping around), which ultimately lead to the death of Tenji's father. Shiho was released because of her father's choice.

Here's a simplified timeline of events:
Tenji & friends play the game -> Tenji gets out and tells his father -> father starts looking around and presumably gets caught -> Shiho and her father somehow get involved (probably because Tenji's father may have entered a game to get information and his friend, Shiho's father, was probably pulled in when he was in a losing position similar to how if you owe money the bank or whoever will reach out to your family members/contacts to pay the deficit) ->Shiho's father chooses to save Shiho instead of Tenji's father -> Tenji's father's death was announced, Shiho's father labeled it as suicide, which didn't make sense to Tenji -> Tenji started to gather information on Shiho because he lost two important things to him tied to her (His friends and father) and got everyone into the game in order to try and expose her (although we now know there was at least one other person who also got them in,kokorogi, since their initial debt was higher) -> present day

That being said I do think Shiho was just unfortunate to become the target of two insane kids (rather than that she asked them to rack up so much money, the two of them probably did it thinking it's for her even even though she didn't ask for it), and her father made a decision that any normal parent would choose. While I don't think Shiho's father labeling it as a suicide was the greatest idea, even though he probably did that because he didn't know Tenji knew about the game and there wasn't enough evidence to prove a murder occurred so he just picked an answer he thought would satisfy a kid.

Ooh, that makes a lot of sense... thank you I was very confused about it. So Tenji pretended to be Ok and acted innocent even after the game and started following Shiho around. And Shiho also pretended like nothing happened. Then how did she get scars? They said she had a plastic surgery because of an accident and I think she still has scars even now. Maybe they are from the kidnapping incident. ╮(￣▽￣)╭

Not at all! It's true that Tenji pretended nothing happened/at least didn't tell Shiho, but also remember they're childhood friends so in a way he was already following her before, just not trying to find information on her. As for Shiho, I don't think she knew why at the time that Tenji himself was related to her being kidnapped, so until she noticed Tenji was spying on her she wasn't really pretending nothing happened since she didn't know what happened. At the present, she knows Tenji has been trying to find information on her but only because she now knows the odd situation around Tenji's father's death and the weird things her kidnapper said were related to the game and the fact that her father's answer to him back then calling it suicide didn't make sense. I don't think she knows that Tenji's old friends had feelings for her and that another reason to Tenji's behaviour was because ever since they met her their priorities changed drastically in a negative way.

As for the scars I completely didn't notice them and at the moment I don't know where they talked about that (if you remember around which chapter it was at I can go refresh my memory) so I can't really give any explanation for that ^^; but it's not unlikely that they came from kidnapping incident

The scar was probably in the shino(the rich guy in Yuu's group) trial for been accused of killing his own father. He kinda almost rape Shiho...but didn't after seeing the scar on her body and she left. And the plastic surgery part was at the second game where they had to write others secret or your owns to complete the game, and I am not sure who but I think it's boobs girl(or Tenji) wrote that Shiho had plastic surgery before and Shiho panicked a lot.

Oh I see. I mean plastic surgery is not something people are usually very proud about right? People might view a person as being kind of fake in a way because that's not how they really look. In a game like this, anything unusual could be taken the wrong way and she could have been panicking because she was worried they would take that comment as in "she did something criminal and had to change her appearance so she isn't caught". In other words, the Shiho that they know is not the "real" Shiho

As for the scar it is a possibility it was from the kidnapping since the scene where Shiho is in the hospital shows she has physical injuries on her head and cheek so it's possible she was also hurt somewhere else too. However I still don't think the chance is too high because if it was a scar that was so bad Shibe who proposed the idea of raping her backed out upon seeing the scar, it must have been serious, and in the kidnapping chapter there was no indication she got seriously injured. Seeing how deeply involved Shiho is with the Tomodachi Game and how there's gaps in the information about her life leading to the present, it's not impossible there may be another accident that hasn't been brought to light yet.

Hi, so I have just read some first few chapters of this manga, but I more or less know the entire plot (I'm afraid to read stories like this, but want to know the full plot). So, have we known why tye Tomodachi Game is there in the first place? What is its purpose? And why people keep getting caught to playing the game?

Sorry to disappoint but no we do not know any of those information.

1) We don't know who created the Tomodachi Game (i.e. the boss of the company). Maybe it's just me not reading carefully enough or that the series has been ongoing for so long I can't remember every single detail, but we haven't been given any hints as to who it could be.

2) Although we do learn the reasonings behind why certain individuals got into/started a round of the Tomodachi Game (as the story progresses, the main 5 meet other groups of people from their own Tomodachi Game), we don't know the overall purpose behind it from the grand scheme of things.

3) There are many different reasons and it depends on the individuals as you will see as you progress through the story. From what we've seen so far, the people on the staff side of the game are not the ones to reach out and invite people to join, rather desperate people seek them out. One reason that seems to come up often is money. Someone is in a great deal of debt and the game is the chance to either generate money to pay it off or shift it to another person.

As of ch 83 which I read before responding, the story does not seem like its near the end at all. Maybe 55 or 60% towards completion.